Ring-shaped granuloma: causes, symptoms, diagnosis, treatment

Granuloma annulare is a benign, chronic, idiopathic condition characterized by the presence of papules and nodules that, through peripheral growth, form rings around normal or slightly atrophic skin.

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What causes granuloma annulare?

The cause of annular granuloma is unknown. Apparently, it is polyetiological, its development may be affected by infections, primarily tuberculosis and rheumatism, endocrine disorders, mainly diabetes mellitus, injuries (insect bites, sunburn, etc.) and other adverse effects, including medications, in particular vitamin D. According to OK Shaposhnikov and I.E. Khazizov (1985), annular granuloma is a dermatopathological sign of carbohydrate metabolism disorder, accompanied by microangiopathies.

Pathomorphology of granuloma annulare

In the middle part of the dermis there are foci of connective tissue necrobiosis in the form of granular destruction, surrounded by a histiocytic infiltrate with a palisade-like arrangement of histiocytes, among which there are lymphocytes, plasma cells, neutrophilic granulocytes and fibroblasts. Destruction of collagen fibers can be complete in the form of one or several areas of necrosis or incomplete in the form of several very small foci. Foci of incomplete destruction are usually small, some bundles of collagen fibers in them look normal, others in a state of varying degrees of destruction acquire a basophilic color, resembling areas of mucoid swelling. In the infiltrate - lymphoid cells, histiocytes and fibroblasts. In the affected areas, collagen fibers are located in different directions, the mucinous material has the form of thin threads and granules, metachromatically stained with toluidine blue. Sometimes single giant cells can be seen. Some authors consider the presence of eosinophils in the infiltrate to be pathognomonic for this disease.

Annular granuloma with very small foci of incomplete destruction of collagen fibers and minor infiltration around may not be noticed due to the vagueness of the histological picture, but the diagnosis can be made based on the presence of histiocytes among the collagen bundles and the abnormal arrangement of the latter.

The epidermis is mostly unchanged, except in cases of superficial necrotic lesions, when the epidermis is ulcerated (perforating form). The infiltrate in these cases is weak, consists of lymphocytes and is located perivascularly around the necrotic lesion; giant cells are rare. Mucin is detected when stained with mucicarmine and alcian blue; lipid deposition is observed in old lesions. Staining for lysozyme and metalloproteinase inhibitor-1 gives a characteristic distribution of the positive reaction, which differs from other types of necrobiotic granulomas, which allows differential diagnosis, including with lipoid necrobiosis.

Electron microscopy reveals collagen fiber remnants, cell fragments, fibrin, and amorphous granular material in the necrobiosis zone; granular destruction of collagen fibrils, thin glycosaminoglycan threads, and infiltrate cells in the transition zone; and histiocytes, epithelioid cells, fibroblasts, and tissue basophils with large granules in the infiltration zone.

Subcutaneous nodes (deep form) of annular granuloma are characterized by the presence of large foci of complete destruction of collagen with palisade-like histiocytes around them. The areas of destruction are usually pale in color, homogeneous, infiltrated with fibrinocyte masses, surrounded by a significantly pronounced chronic infiltrate consisting mainly of lymphocytes.

The histogenesis of granuloma annulare is unknown. Immunofluorescence microscopy revealed deposits of IgM and complement component C3 in the walls of small vessels of the lesion, partially also in the dermal-epidermal junction together with fibrinogen, and in the necrotic lesion together with fibrin. It is suggested that tissue changes may initially be similar to those in the Arthus phenomenon, and then delayed-type hypersensitivity leads to granuloma formation. Immunomorphological examination revealed activated T-lymphocytes in the infiltrates, predominantly with the helper/inducer phenotype, as well as CD1-positive dendritic cells similar to Langerhans cells; they probably play a role in the pathogenesis of the disease. Localized and disseminated forms of the disease are believed to have different genesis. HLA-BW35 is often detected in the second form. Its association with antibodies against thyroid globulin has been found. Familial cases have been described.

Symptoms of Granuloma Annulare

Erythematous lesions of yellowish, bluish color most often occur on the back of the feet, shins, hands and fingers, are usually asymptomatic. Annular granuloma is not associated with systemic diseases, except that the frequency of sugar metabolism disorders is higher in adults with multiple rashes. In some cases, the causes of the disease are exposure to sunlight, insect bites, skin tests for tuberculosis, trauma and viral infections.

Clinically, the typical form of the disease is manifested by a monomorphic rash consisting of small, slightly shiny painless nodules of a reddish or pinkish color, sometimes the color of normal skin, grouped in the form of rings and semirings with a preferred localization on the back of the hands and feet. The rash is usually not accompanied by subjective sensations and, as a rule, does not ulcerate. The central part of the lesions is somewhat sunken, cyanotic, looks as if slightly atrophic, more pigmented than the peripheral zone, in which individual closely spaced nodules are detected. Other variants are less common: disseminated annular granuloma, developing in individuals with carbohydrate metabolism disorders, characterized by rashes of a large number of papules, located separately or merging, but rarely forming rings; perforating form with skin lesions of the distal parts of the extremities, especially on the hands, less often - the face, neck, trunk. Formation of scars is possible at the site of regressed elements.

Deep (subcutaneous) form, generalized or localized, resembles rheumatic nodules, develops almost exclusively in childhood, nodes appear in the subcutaneous tissue, most often on the legs, as well as on the scalp, palms. In rare cases, adults have single annular lesions on the face, mainly on the forehead. Other atypical variants are also observed (erythematous, tuberous, follicular, lichenoid, actinic). The typical form of annular granuloma occurs mainly in children, more often in girls. In most cases, annular granuloma regresses, although relapses are possible.

Treatment of Granuloma Annulare

Granuloma annulare usually does not require treatment, the rash resolves spontaneously, but topical glucocorticoids with occlusive dressings and intralesional glucocorticoids may be used. PUVA is effective in patients with disseminated forms of the disease.