Pseudopelada, or atrophic focal alopecia areata.

The term pseudopelade, or atrophic focal alopecia, is used to denote small-focal slowly progressing cicatricial atrophy of the scalp with irreversible hair loss without pronounced perifollicular inflammation. In most cases, using clinical, histological and other necessary research methods, it is possible to prove that cicatricial atrophy is the end result of the evolution (sometimes very long) of a number of known dermatoses localized on the scalp. First of all, these are atrophic forms of lichen planus, discoid lupus erythematosus, limited scleroderma, decalvans folliculitis, or lupoid sycosis. Much less frequently, focal atrophic alopecia can be caused by diseases such as follicular mucinosis, Langerhans cell histiocytosis of the skin, lipoid necrobiosis, annular granuloma, sarcoidosis, metastases to the scalp of tumors of internal organs, localized cicatricial pemphigoid, favus, etc. In these cases, atrophic alopecia is the final symptom of a number of skin diseases, and not an independent dermatosis. Therefore, R. Degos et al. (1954) proposed to call the final result of the evolution of a number of acquired dermatoses on the scalp a condition of pseudopelade, indicating the specific disease that caused it.

However, it is not always possible to determine the type of dermatosis that caused the development of focal alopecia. In these cases, it is considered possible to make a preliminary diagnosis of "Broca's pseudopelade". Further clinical and histological observation of such a patient (sometimes very long-term) can help to determine (including by the method of exclusion) a specific dermatosis that led to focal atrophic alopecia. Significant diagnostic difficulties are associated with the fact that the manifestations of a number of known dermatoses at their debut on the scalp differ little clinically, and their similarity is present not only at the stage of pseudopelade formation (the final stage), but also in the active stage of the dermatosis and is manifested in the dominance of scleroatrophic processes in the affected skin.

Symptoms of Pseudopelada

In 1885 Brocq (Brocq L.) described pseudopelade (pelade - French - circular baldness) as a separate nosological form, giving its clinical and evolutionary characteristics. Contemporaries unanimously accepted this concept and began to study the histological features of pseudopelade. It is considered a rare disease (condition); it occurs mainly in middle-aged women, sometimes in children. The onset of the disease often remains unnoticed due to the lack of subjective sensations. Unexpectedly for the patient, multiple small foci of atrophic baldness are discovered. In the initial period of the disease, they are small, isolated, round or oval from 5 to 10 mm in size.

These foci may increase in size, merge into larger irregularly shaped foci and always stand out sharply from the surrounding scalp. Usually the number and size of foci increase slowly, but they may remain localized for a long time. In their location and outlines they have been compared to "an archipelago of islands on a geographical map", "tongues of flame", "thawed patches in the snow", "fingerprints white with flour", etc. Alopecia foci have different sizes, but with peripheral growth and fusion (very slowly, over a number of years) they acquire semicircular, scalloped contours. The skin surface in bald areas is smooth, white, atrophic, without follicular skin pattern and peeling. Side lighting reveals the smoothness of the surface and its shine. Atrophic areas are somewhat sunken, not compacted. Individual remaining hair tufts are often visible within them. Atrophic alopecia occurs spontaneously, without any preceding inflammatory manifestations, which distinguishes it from the formation of similar alopecia in favus.

There is no folliculitis along the periphery of pseudopelade foci, as is the case with decalving (epilatory) folliculitis. Mild reddening of the skin around the hair is rare, mainly in the initial stage of the disease and is short-lived. The hair that borders the visible foci of atrophy is of normal length and color. Sometimes in this zone, in the area of the external openings of the hair follicles, the areas of hair near the surface of the skin are colored darker and acquire the appearance of tattoo dots at the mouths of the follicles or the color of licorice root (R. Degos, 1953). Patients usually do not find fallen hair on the pillow or in hats. However, with progression, pulling the hair in the marginal zone of the lesion leads to its easy removal. The roots of the removed hair are surrounded by juicy translucent whitish muffs. The course of pseudopelade is chronic, slowly progressing. After 15-20 years, hair may still remain that is able to cover existing defects. In some cases of subacute course, the spread of atrophic alopecia is much faster and can lead to almost complete cicatricial alopecia in 2-3 years. Patients only occasionally complain of a feeling of tension in the affected skin, and even more rarely of slight itching. Usually, complaints about a cosmetic defect predominate, which leads to psychological trauma.

Histopathology

In the early stages of pseudopelade, only a massive perifollicular and perivascular lymphocytic infiltrate with single histiocytes is detected, which is usually located around the upper and middle third of the follicle, without affecting its lower part; the infiltrate penetrates the walls of the follicles and sebaceous glands, gradually destroying them. In the late stages of development (in old foci), the epidermis is atrophic, the epithelial outgrowths are smoothed out. Changes in the dermis are characterized by fibrosis, death of elastic fibers, necrosis of hair follicles and sebaceous glands. Bundles of collagen fibers are distinguished, passing vertically to the skin surface, and sweat glands and muscles that raise the hair are usually preserved.

Broca's concept of pseudopelade as an autonomous disease gradually began to change. At first, the concept of pseudopelade was expanded. It successively included Kenco's decalvans folliculitis and spotted atrophy of the scalp associated with follicular keratosis (spiny lichen) (Rabut, 1953 and Prieto G., 1955). In 1955, Prieto Gay, discussing the origin of pseudopelade, rightly asserted that spotted atrophy as a result of damage to the hair follicles on the scalp can be caused by lichen planus, lupus erythematosus, and scleroderma. Thus, as knowledge of the clinical variants of some known dermatoses expanded, it became clear that the changes in the scalp caused by them differed little from the manifestations of classical pseudopelade. Therefore, it became impossible to give an accurate clinical and histological description of pseudopelade as a final symptom common to a number of skin diseases, and not an independent dermatosis (Degos R., 1953). To a large extent, they are determined by the dermatosis that caused focal atrophic alopecia, and are a stage of its development. Skin diseases that cause the condition of pseudopelade much more often affect other areas of the skin, sometimes visible mucous membranes. Therefore, it is important to carefully examine the patient's entire skin, visible mucous membranes and nails. Any manifestations detected outside the foci of atrophic alopecia on the head should be determined morphologically, histologically and nosologically. Clarification of the diagnosis will allow the doctor to orient himself in the genesis of pseudopelade and prescribe adequate therapy. In those cases when, using anamnesis, clinical picture and pathomorphology, it is not possible to establish the dermatosis that caused focal atrophic alopecia. Broca's pseudopelade is diagnosed as a disease of unknown etiology. It should be taken into account that the dermatosis that causes pseudopelade in some cases can only be diagnosed with long-term clinical and histological observation of the patient.

Pseudopelade should first of all be differentiated from alopecia areata, since their treatment and prognosis are different. In alopecia areata, the mouths of the hair follicles are preserved, there is no skin atrophy, so hair growth is usually restored. In addition, in the marginal zone of the lesion of alopecia areata (circular) there are hairs in the form of exclamation marks. They are shortened to 3 mm, their distal edge is rough, split, and the proximal edge is thinned downwards and ends in a whitish club-shaped thickened hair cone. This is a pathognomonic sign for alopecia areata.

Rational treatment of patients with pseudopelade is difficult to carry out. It is advisable to conduct a detailed examination to identify hidden concomitant diseases (chronic foci of infection, especially in the mouth, in the sinuses of the nose and ears, endocrine disorders, etc.). Courses of antimalarial drugs are recommended, justifying this by a positive therapeutic effect in dermatoses that often cause the condition of pseudopelade (lichen planus, discoid lupus erythematosus, scleroderma, etc.). If the therapeutic effect of general treatment is insufficient, or it is impossible to carry it out, it is possible to use intradermal injection into the marginal (active) zone of the lesion of a crystalline suspension of triamcinolone (1 ml of Kenalog-40), diluted 3-5 times with a 2% solution of lidocaine. External use of a cream (ointment) with a glucocorticosteroid is also possible.

If a noticeable pseudopelade has formed, it is recommended to model the hairstyle accordingly, wear a hairpiece or wig, and perform surgical correction (autotransplantation of hair into the atrophic area or removal of areas of skin with cicatricial alopecia).

Pseudo-pelade state

Many clinical observations have convincingly shown that during the formation of pseudopelade, the manifestations of various dermatoses on the scalp - atrophic forms of lichen planus, lupus erythematosus, scleroderma, decalvans folliculitis (lupoid sycosis), etc. - differ little. At the same time, the rashes of these dermatoses in other localizations retain their characteristic symptoms, therefore they differ from each other.

The difficulties in diagnosing diseases that cause pseudopelade are determined by the appearance of a common property in different dermatoses on the scalp, which manifests itself in the smoothing of their characteristic symptoms and the reduction of clinical differences. Focal atrophy of the scalp with hair loss becomes common and dominant in the clinical picture. All this leads to the "single-facedness" of a number of diseases on the scalp, the similarity of their clinical manifestations not only in the remission stage, but also in the active period.

When pseudopelade is combined with rashes in other localizations, the physician's focus on a single genesis of these manifestations is justified. Establishing a diagnosis of rashes on the skin of the trunk, limbs or visible mucous membranes predetermines the genesis of the existing pseudopelade in most cases. In cases where the cause of atrophic alopecia is proven, the pseudopelade condition is stated with an indication of the specific disease that caused it. For example, the pseudopelade condition caused by the follicular form of lichen planus (or discoid lupus erythematosus, etc.). In these cases, atrophic cicatricial alopecia occurs secondarily and is the final symptom of a number of skin diseases, and not an independent dermatosis. Early diagnosis of dermatosis allows for timely prescription of appropriate treatment, which stabilizes the disease and stops the progression of alopecia, but does not restore lost hair.

To establish the disease that caused the pseudopelade condition, it is important to obtain a detailed anamnesis, carefully examine the entire patient, conduct microscopic, microbiological and histological studies, and in some cases - long-term observation in dynamics. When examining the scalp, special attention is paid to the zone bordering the focus of atrophic alopecia. The presence of hyperemia, peeling, altered hair (broken, with sheaths at the base, deformed, of a different color), yellow scaly crusts in the form of a shield around the base of individual hairs, follicular pustules and inflammatory nodes, purulent-bloody crusts, small scars and larger foci of atrophic alopecia, separately or in combination, allow the doctor to suspect and then exclude mycosis of the scalp.

Pay attention to the horny "plugs" in the mouths of hair follicles on the skin directly adjacent to the focus of atrophic baldness. Their formation is possible with the follicular form of lichen ruber follicularis decalvans, discoid lupus erythematosus, nodular elastosis with cysts and comedones (syn. actinic elastosis, or Favre-Racouchot disease), follicular dyskeratosis Darier, keratosis follicularis spinosus decalving.

Inflammatory (nodules, pustules and knots) and non-inflammatory elements can form on the scalp. Thus, when folliculitis is detected around the atrophic baldness lesion on the head, the presence and number of pustules, their connection with hair follicles, the formation of erosive-ulcerative defects and purulent-bloody crusts should be determined. Folliculitis and pustules in this localization are found in decalcifying folliculitis and its clinical variant - lupoid sycosis mycosis of the scalp. Chickenpox and shingles, necrotic acne, erosive pustular dermatosis of the scalp and eosinophilic pustular folliculitis are manifested by the formation of pustules on the scalp. Inflammatory nodes on the scalp with subsequent formation of normal or atrophic scars with baldness can occur with the infiltrative-suppurative form of mycosis, Majocchi's mycotic granuloma, undermining and abscessing perifolliculitis and Hoffmann's folliculitis of the head.

Non-inflammatory nodules and knots are formed in benign and malignant neoplasms of the skin and its appendages. In the lesions, hair follicles are replaced by newly formed tissue, sometimes they are destroyed by ulceration. Numerous large sebaceous hair follicles located in the scalp predetermine, all other things being equal, a high frequency of tumors originating from them. Early-onset baldness of the frontal-parietal region in men leads to excessive exposure to sunlight and other adverse external factors on areas of the skin unprotected by hair, which causes the development of dystrophic changes (dyschromia, telangiectasias, elastosis and atrophy) and predisposes to malignant neoplasms.

Telangiectasias in the area of atrophic alopecia may form in discoid lupus erythematosus, poikilodermic lymphoma of the skin, actinic keratosis, X-ray dermatitis, and lipoid necrobiosis.

Histological examination of the affected skin is of great importance in diagnosing the dermatosis that caused the pseudopelade condition. The correct choice of the biopsy site determines the success of this study, which is important for clarifying the diagnosis. The skin site should be chosen in the border zone with the pseudopelade, where there are active clinical manifestations of the dermatosis. A biopsy performed within the boundaries of long-established atrophic alopecia or in the inactive stage of the disease does not contain useful information and therefore will not help in diagnosing the dermatosis.

The clinical manifestations, histopathology and differential diagnosis of dermatoses that most often lead to the pseudopelade condition will be described below.

Dermatoses leading to pseudopelade state

Atrophic forms of lichen planus

There are three known atrophic clinical forms of lichen planus, which with varying frequency can lead to focal cicatricial atrophy of the skin, including on the scalp, i.e. to the pseudopelade condition. These include follicular decalvans lichen (lichen ruber follicularis decalvans, synonyms: lichen ruber acuminatus, Hebra F.1862; Kaposi, M.1877; lichen planopilaris, Pringle JJ1895; lichen spinulosis et folliculitis decalvans, Little.G. 1930; lichen planus et acuminatus atrophicans, Feldman E.1922,1936), atrophic lichen planus (lichen planus atrophicans, Hallopeau H. 1887) and vesicular (pemphigoid) lichen planus (lichen ruber planus bullosus /pemphigoides, vesiculosus).

Follicular decalvans lichen ruber

In follicular decalving lichen ruber (FDCL), the scalp is affected more often than in other dermatoses. Some authors claim that in 90% of cases pseudopelade is caused by lichen ruber planus (Prieto Gay, 1955; Kaminsky et al., 1967, etc.). Others (Silver et al., 1953), having summarized literature data (101 cases) and 4 of their own observations, cite a 2-fold lower frequency (42%) of atrophic alopecia on the scalp.

Symptoms

Most often, this clinical form of lichen planus develops at the age of 30-70 years, although there are cases of earlier onset. Most patients with lesions on the scalp are middle-aged women. Follicular decalvans lichen ruber can begin with lesions of the scalp or trunk and limbs. On the head, the initial lesion most often occurs in the parietal region. These are usually small, about 1 cm in diameter, foci of mild hyperemia and flaking, irregular in shape with diffuse hair loss. It is hair loss that is usually the reason for visiting a doctor. Gradually, within the affected areas, the skin becomes pale, smooth, shiny, taut, the follicular pattern is smoothed out, the hair falls out completely - cicatricial atrophy develops. However, within the atrophied areas, individual hairs are preserved in places, sometimes - tufts of hair. In the active stage of the disease, there is slight thinning of hair of irregular outlines and separate follicular scale-crusts, which merge in places, along the edges of the lesions. The hair in the circumference of the lesion of cicatricial atrophy is mostly preserved, but is easily epilated and glassy muffs 3 mm long are visible on their root parts. Sometimes, along the edge of the lesions, you can find separate small cone-shaped follicular nodules and horny follicular "plugs". The latter resemble "black dots" - low broken hairs in the chronic form of trichophytosis.

When comparing the described manifestations with the picture of the "classic" pseudopelade, it is easy to notice their great similarity. The lesion of the scalp (the pseudopelade condition) can exist for a long time (from several months to 2-5-10 years or more) in isolation, slowly progressing and sometimes fading. With a long-term low-symptom course of the dermatosis, the formation of noticeable foci of skin atrophy on the scalp can occur many years after its debut. This significantly complicates the diagnosis of this rare form of lichen planus. At the same time, with the formed pseudopelade condition, the possibility of progression of the process without visible inflammatory phenomena (hyperemia and follicular papules) of the circumference and within the focus of atrophic alopecia is clearly manifested. In this case, only an increase in its area in the parietal, occipital or temporal regions indicates the progression of the dermatosis.

The number of rashes on other areas of the skin varies widely. Small, 1-2 mm in diameter, flesh-colored or pale pink follicular papules with small horny spines on the top appear mainly on the extensor surface of the limbs and trunk. They are usually isolated, only merging into small plaques in certain areas. Sometimes follicularly (perifollicularly) located papules have a rich red, stagnant color. Pointed horny plugs in the center of the papules can be of different sizes, but usually do not exceed 1-1.5 mm in diameter. They are dark brown or black in color and resemble comedones in seborrhea in appearance. Unlike comedones, horny spines are dense, protrude above the skin level and create a grater-like impression when stroking the surface (a sign characteristic of "spiny lichen" - lichen spinulosus). With a certain amount of effort, the hyperkeratotic spine (cone, plug) can be removed with tweezers, revealing the widened and deepened opening of the hair follicle. After the resolution of follicular papules, scleroatrophic changes remain in some cases, which manifest themselves to varying degrees in different areas of the skin. Thus, a clearly visible atrophic alopecia (psedopeladic condition) always forms on the scalp. Hair also falls out on other areas of the body, but distinct cicatricial changes are usually not clinically visible. This applies primarily to hair loss in the pubis and axillary areas. As histological studies have shown, such changes are explained by the death of hair follicles without pronounced signs of atrophy of other skin structures and integumentary epithelium. Thus, at the site of follicular papules in the armpits, on the pubis and in other areas of the lesion, hair loss is caused by scleroatrophic changes, but clinically this baldness is perceived as non-scarring.

In some patients with this dermatosis (about 10%), the nail plates are also affected (thinning, longitudinal striations, fragility of the peripheral edge, pterygium, sometimes atrophy).

Thus, clinical manifestations of follicular decalvans lichen ruber may begin with the scalp and be limited to it for a long time (pseudopelade condition), or be accompanied by rashes of follicular spiny papules on the skin of the trunk or extremities. At the same time, typical papules of lichen ruber planus may be present on the skin or visible mucous membranes, however, this is rare.

In the literature, the combination of atrophic alopecia of the scalp, alopecia in the axillary areas, on the pubis and follicular spinous papules on the trunk and limbs has long been known as the Picardy-Lassuer-Little syndrome. The characteristic clinical manifestations of this syndrome are the result of the evolution of follicular papules of one dermatosis - the follicular form of lichen planus. Individual symptoms of this triad or incomplete combinations of them are encountered in clinical practice more often than a combination of all three at the same time.

Currently, dermatologists have formed an almost unanimous opinion about Picardy-Lassuer-Little syndrome as a manifestation of atypical lichen planus (its follicular form), which is diagnosed in patients in the late stages of the development of this dermatosis.

Histopathology of a follicular papule with a horny plug on smooth skin at an early stage: the epidermis is unchanged, the hair follicle is dilated and filled with a horny plug, wedge-shaped hypergranulation of the follicular funnel is expressed, vacuolar degeneration of cells at the border of the follicle epithelium and dermis; lymphocytic-histiocytic infiltrate is located mainly perivascularly and perifollicularly. Under the epidermis, in places, there are ribbon-like infiltrates of lymphoid cells-histiocytes that erase the border between the epidermis and dermis; infiltrate cells penetrate into the external hair sheath in its root part. At a late stage of development: varying degrees of epidermal atrophy. The epithelial outgrowths are smoothed out, the number of lymphocytes and histiocytes located perivascularly and perifollicularly is reduced in the dermis, with pronounced fibrous manifestations; there is periinfundibular fibroplasia and gaps between the thinned follicle and damage to the dermis, fibrous strands replacing the deteriorating hair follicles, while sclerosis in the interfollicular areas of the dermis is absent.

Diagnosis of pseudopelada

When atrophic alopecia foci are detected on the scalp, it is necessary to first exclude dermatoses, which most often lead to the pseudopelade condition. An objective examination of the patient begins with an examination of the area bordering the pseudopelade. Then, the entire surface of the skin, hair, nails, and visible mucous membranes are examined sequentially. When rashes are detected, the morphology of the primary rash element and its characteristics (color, size, shape, surface condition, connection with the hair follicle and the presence of keratosis in the center, etc.) are determined. It is necessary to take into account the predominant localization of the rash and the formation of rash elements at the sites of injury (positive isomorphic reaction). If necessary, a histological examination of the affected skin is performed. Diagnosis of dermatosis, manifested by rashes on smooth skin and the scalp, allows the doctor to reasonably navigate the origin of atrophic alopecia on the scalp.

In isolated atrophic alopecia on the scalp, diagnostic capabilities are limited due to the scarcity and erasure of active clinical manifestations of dermatoses in this localization and the virtually identical final result of their evolution - the pseudopelade state. It is necessary to study the anamnesis, histological examination of the active lesion and long-term observation of the patient in dynamics.

Differential diagnostics

The rash of pointed follicular (perifollicular) papules on the skin of the trunk and extremities in FDCL is differentiated from similar manifestations of some acquired and congenital dermatoses: red pityriasis versicolor pilaris, follicular keratosis (or pityriasis versicolor), lichenoid (miliary) syphilid, small-nodular sarcoidosis, lichenoid tuberculosis of the skin, lichenoid trichophytid, follicular psoriasis, follicular spinous decalvans keratosis of Siemens (Siemens syndrome) and some other inherited dermatoses accompanied by follicular keratosis.

Follicular decalvans lichen ruber (FDCL) differs from Devergie's pityriasis rubra pilaris (DPR) by, firstly, the absence of superficial erythematous-squamous psoriasiform plaques, which in DPR form closely grouped follicular conical papules of a yellowish-red color; secondly, the absence of follicular papules with dark large horny cones in the center on the dorsum of the fingers; thirdly, patients with FDCL do not have keratosis of the palms and soles, as well as erythematous-squamous, confluent lesions of the face and a tendency to erythroderma. In FDCL, in addition to follicular papules, papules typical of lichen planus may be simultaneously detected on the skin and visible mucous membrane, as well as pseudopelade and hair loss in the axillary areas and pubis.

FDCL differs from follicular keratosis (lichen planus) by follicular spinous papules that have a perifollicular infiltrate, are grouped and may be accompanied by itching. FDCL is not characterized by predominant lesions of the skin of the buttocks and extensor surface of the shoulders, as well as a combination with acrocyanosis, xerosis and atopy. In addition to follicular papules, FDCL can also develop papules typical of lichen planus on the skin (flat, polygonal, shiny, pinkish-purple with an umbilicated depression in the center and a characteristic whitish-grayish mesh standing out on the surface) and visible mucous membranes. Some patients with FDCL also develop a condition of pseudopelade, hair loss in the axillary areas and on the pubis. FDCL usually develops in adulthood rather than in childhood, has a characteristic evolution and recurs, rather than existing monotonously, for a long time without significant dynamics.

From miliary syphilid, or syphilitic lichen, which manifests itself as follicular nodules of a rich reddish-brown color, FDCL is distinguished by the flesh-colored or pale-red color of follicular spiny papules, usually located symmetrically (and not in a distinct grouping) and sometimes accompanied by itching. With FDCL, there is no jerky rash and other manifestations of secondary syphilis (lenticular papules in characteristic areas on the skin, mucous membranes of the mouth and genitals, polyadenitis, leukoderma, non-scarring alopecia on the scalp), serological reactions to syphilis are always negative

Unlike the now rare lichenoid tuberculosis of the skin, lichen scrofula, FDCL usually occurs in adults (and not in childhood or adolescence), is not accompanied by manifestations of cutaneous and organ tuberculosis, exists for a longer time (more than 2-3 weeks), and may be accompanied by itching. With FDCL, spiny follicular papules are usually not grouped on the lateral surfaces of the body and do not merge into coin-shaped plaques of a yellowish-brown color, slightly scaly and slightly infiltrated, as in seborrheic dermatitis. According to FDCL, the existence of papules on the skin and visible mucous membrane typical of lichen planus, pseudopelade, hair loss in the axillary areas and on the pubis, and lesions of the nail plate are also possible. The results of the histological examination of the affected skin, which vary significantly, are of decisive importance. In follicular decalving lichen ruber, perifollicular and perivascular infiltrates do not have a tuberculoid structure.

FDCL differs from the small-nodular form of sarcoidosis of the skin by its pointed follicular papules with horny spines in the center (with this form of sarcoidosis, the papules are hemispherical, smooth with a small central depression), the absence of the “dustiness” phenomenon during diascopy (it is revealed in sarcoidosis as tiny yellowish-brown specks-dust, reminiscent of the “apple jelly” symptom in lupus tuberculosis of the skin), the absence of a pronounced grouping, the rarity of localization on the face and itching, which can accompany the rash. It is also necessary to take into account the papules on the skin and oral mucosa that are typical for lichen planus (in sarcoidosis, lesions of the oral mucosa are rare, pseudopelade is possible, hair loss in the armpits and pubis, changes in the nails and the absence of systemic lesions characteristic of sarcoidosis (mediastinal lymph nodes, lungs, liver, visual organ, bones, etc.). The histological picture of these dermatoses is different: in sarcoidosis, a typical epithelioid cellular granuloma is found in the dermis.

Manifestations of FDCL on the skin of the trunk and extremities are morphologically similar to lichenoid trichophytid. It is easy to distinguish them, since the latter occurs with active irrational treatment of patients with infiltrative-suppurative, less often - superficial form of trichophytosis. Skin rashes with FDCL do not occur as a fleeting outbreak, are not accompanied by general symptoms (fever, chills, malaise, leukocytosis) and do not disappear without a trace after 1-2 weeks, which is typical for secondary infectious-allergic rashes in trichophytosis - trichophytids.

FDCL differs from the rare follicular form of psoriasis by slightly different characteristics of the follicular papule. Thus, with FDCL, deep in the center of the papule lies a comedone-like horny spine, which cannot be removed by scraping, there is also perifollicular infiltration. When scraping a psoriatic follicular papule, a silvery-white scale with a small superficial spine on the back easily comes off its surface, and perifollicular infiltration is not determined. In some cases, the presence of scaly lenticular papules and plaques in areas typical for psoriasis simultaneously allows reproducing the symptoms of the psoriatic triad. It is also necessary to take into account the papules on the skin and oral mucosa that are typical of lichen planus, the possible existence of pseudopelade, hair loss in the armpits and pubis, and characteristic nail damage. It should be taken into account that the very rare follicular psoriasis develops mainly in children after tonsillitis or other streptococcal infection and is localized mainly on the trunk. The histopathological changes that form follicular papules in these dermatoses also differ.

Follicular papules in FDCL, unlike similar elements of follicular dyskeratosis (FD) Darier, have a pointed shape, pale pink or red color, do not erode or vegetate, do not group or merge into plaques on seborrheic areas and in large folds of the skin, affect the extensor surfaces of the limbs, trunk and scalp. In FDCL, atrophic alopecia often develops on the scalp, hair falls out in the armpits and pubis, which does not happen with FD. It should also be taken into account that FD usually begins before puberty (and FDCL - usually after), has a long relapsing course, can be accompanied by mental disorders, hypogonadism, increased sensitivity to UV rays and a tendency to the addition of pyogenic and viral infections in the lesions. Pathomorphological changes in these dermatoses also differ significantly. Dyskeratosis, follicular hyperkeratosis and suprabasal acantholysis, leading to the appearance of suprabasal lacunae with uneven proliferation of dermal papillae in them, are very characteristic of FD.

The manifestations of FDCL and follicular mucinosis (FM) differ significantly, despite the partial similarity of localizations (scalp, limbs). Thus, follicular papules in FM do not have such pronounced follicular keratosis as nodules in FDCL, they crowd and merge into small oval erythematous-squamous plaques with an emphasized follicular pattern and weak infiltration. Hair falls out within these plaques, but skin atrophy does not occur, which is not typical for FDCL. It should also be taken into account that the course of FM is long and progressive. At the same time, atrophic alopecia of the scalp, hair loss in the axillary areas and pubis, damage to the nails and mucous membranes do not develop. The histological picture of these dermatoses is also different. FM is characterized by reticular dystrophy of the epithelial cells of the hair follicle and sebaceous glands with the formation of cystic cavities filled with mucin, stained with metachromatic toluidine blue, and perifollicular inflammatory infiltration.

The manifestations of FDCL should be distinguished from the follicular spinous decalvans keratosis (FSDC) of Siemens. Both diseases manifest themselves as follicular acuminate decalvans papules with central horny spines, focal atrophic alopecia of the scalp and similar atrophic changes in the nail plates. However, FDCL is an acquired disease and usually develops in adulthood, more often in women, while FSDC is an inherited disease that appears soon after birth only in males. In FDCL, in addition to follicular spinous papules, a small perifollicular infiltrate on the extensor surfaces of the forearms, trunk and visible mucous membranes may also be typical papules of lichen planus. In addition, some patients with FDCL have hair loss in the axillary areas and on the pubis. In FSDK, miliary pointed papules with spines affect from childhood mainly the scalp, face, and much less the extensor surfaces of the limbs. Focal atrophic alopecia develops at the sites of lesions of the scalp and eyebrows, and atrophoderma on the face. In addition, FSDK, unlike FDCL, is characterized by early damage to the organ of vision (ectropion, conjunctivitis, keratitis, focal keratosis of the palms and soles is possible, and sometimes there is a delay in physical and mental development. Histopathological changes in the affected skin in these dermatoses also differ. In Siemens' FSDK, perifollicular and perivascular lymphocytic-histiocytic infiltrates in the dermis, as well as vacuolar degeneration of cells at the border of the epithelium of the hair follicle and the dermis, are absent.

In childhood, the manifestations of a rare inherited disease - fusiform hair aplasia, or monilethrix, and superficial mycosis of the scalp are very similar. Clinical signs of fusiform hair aplasia usually appear in early childhood in the form of broken hairs (up to 1-2 cm) and horny follicular papules. Due to the disruption of the structure and nodular deformation of the hair shafts, they break off low (a symptom of black dots), first in the occipital region, and then on the entire scalp. In addition, the hair grows poorly, falls out, lacks shine, is twisted, with split ends. This leads to diffuse, less often - focal hair loss. At the same time, the scalp changes: small, densely located, skin-colored follicular horny papules appear (the surface is very reminiscent of goose bumps) and diffuse fine-lamellar scaling. Often accompanied by follicular keratosis of varying severity on the extensor surface of the upper limbs and the back of the neck. With a long course, atrophy of the scalp with hair loss is possible. In these rare cases, pseudopelade is diagnosed and differentiated from other dermatoses that can cause it. From questioning the parents of such children, it turns out that the lesion of the scalp began in early childhood and is hereditary. The clinical picture (hypotrichosis, follicular keratosis), anamnesis and microscopic examination of the hair (areas of its thickening of a dark color alternate with thinned light fragments, resembling a necklace; there are no fungal elements in the hair) allow us to establish a diagnosis. Histologically, follicular keratosis and inflammatory infiltrate in the area of hair follicles are detected in the skin.

A preliminary diagnosis of FDCL must be confirmed by appropriate histological examination results.

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