Muscle atrophy (amyotrophy) of the hand: causes, symptoms, diagnosis

Muscle atrophy (amyotrophy) of the hand in the practice of a neurologist is encountered in the form of secondary (more often) denervation atrophy (due to a violation of its innervation) and primary (less often) atrophy, in which the function of the motor neuron is generally not affected ("myopathy"). In the first case, the pathological process can have different localizations, starting from motor neurons in the anterior horns of the spinal cord (C7-C8, D1-D2), anterior roots, brachial plexus and ending with peripheral nerves and muscles.

One of the possible algorithms for conducting a differential diagnosis is based on taking into account such an important clinical sign as one-sidedness or two-sidedness of clinical manifestations.

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The main causes of hand muscle atrophy:

I. Unilateral atrophy of the hand muscles:

1. Carpal tunnel syndrome with median nerve injury;
2. Neuropathy of the median nerve in the area of the pronator teres;
3. Ulnar nerve neuropathy (ulnar wrist syndrome, cubital tunnel syndrome;
4. Radial nerve neuropathy (supinator syndrome; tunnel syndrome in the upper third of the shoulder);
5. Scalene muscle syndrome with compression of the upper part of the neurovascular bundle;
6. Pectoralis minor syndrome (hyperabduction syndrome);
7. Thoracic outlet syndrome;
8. Plexopathies (others);
9. Pancoast syndrome;
10. Amyotrophic lateral sclerosis (at the onset of the disease);
11. Complex regional pain syndrome (shoulder-hand syndrome, reflex sympathetic dystrophy);
12. Spinal cord tumor;
13. Syringomyelia (at the onset of the disease);
14. Hemiparkinsonism-hemiatrophy syndrome.

II. Bilateral atrophy of the hand muscles:

1. Amyotrophic lateral sclerosis;
2. Progressive spinal amyotrophy distal;
3. Hereditary distal myopathy;
4. Atrophy of the muscles of the hand
5. Plexopathy (rare);
6. Polyneuropathy;
7. Syringomyelia;
8. Carpal tunnel syndrome;
9. Spinal cord injury;
10. Spinal cord tumor.

I. Unilateral atrophy of the hand muscles

In carpal tunnel syndrome, hypotrophy develops in the thenar muscles (in the muscles of the eminence of the thumb) with their flattening and limitation of the range of active movements of the 1st finger. The disease begins with pain and paresthesia in the distal parts of the hand (I-III, and sometimes all fingers of the hand), and then hypoesthesia in the palmar surface of the 1st finger. The pain intensifies in a horizontal position or when raising the hand up. Motor disorders (paresis and atrophy) develop later, several months or years after the onset of the disease. Tinel's symptom is characteristic: percussion with a hammer in the carpal tunnel area causes paresthesia in the area of innervation of the median nerve. Similar sensations develop with passive maximum extension (Phalen's sign) or flexion of the hand, as well as during the cuff test. Autonomic disorders in the hand (acrocyanosis, sweating disorders), decreased conduction velocity along motor fibers are characteristic. In almost half of all cases, carpal tunnel syndrome is bilateral and usually asymmetrical.

Main causes: trauma (often in the form of professional overexertion during heavy manual labor), arthrosis of the wrist joint, endocrine disorders (pregnancy, hypothyroidism, increased secretion of STH during menopause), cicatricial processes, systemic and metabolic (diabetes) diseases, tumors, congenital stenosis of the carpal tunnel. Athetosis and dystonia in cerebral palsy are a possible (rare) cause of carpal tunnel syndrome.

Factors that contribute to the development of carpal tunnel syndrome: obesity, diabetes, scleroderma, thyroid disease, systemic lupus erythematosus, acromegaly, Paget's disease, mucopolysaccharidoses.

Differential diagnosis. Carpal tunnel syndrome sometimes has to be differentiated from sensory partial epileptic seizures, nocturnal dysesthesia, CV-CVIII radiculopathy, and scalene syndrome. Carpal tunnel syndrome is sometimes accompanied by certain vertebrogenic syndromes.

Neuropathy of the median nerve in the area of the round pronator develops due to compression of the median nerve as it passes through the ring of the round pronator. Paresthesia is observed in the hand in the area of innervation of the median nerve. In the same zone, hypoesthesia and paresis of the flexors of the fingers and the muscles of the eminence of the thumb develop (weakness of the opposition of the thumb, weakness of its abduction and paresis of the flexors of the II-IV fingers). Percussion and pressure in the area of the round pronator are characterized by pain in this area and paresthesia in the fingers. Hypotrophy develops in the area of innervation of the median nerve, mainly in the area of the eminence of the thumb.

Neuropathy of the ulnar nerve (ulnar syndrome of the wrist; cubital tunnel syndrome) is in most cases associated with tunnel syndrome in the elbow joint (compression of the nerve in the cubital canal of Mouchet) or in the wrist joint (Guyon's canal) and is manifested, in addition to atrophy in the area of the IV-V fingers (especially in the hypothenar area), by pain, hypoesthesia and paresthesia in the ulnar parts of the hand, a characteristic tapping symptom.

Main causes: trauma, arthritis, congenital anomalies, tumors. Sometimes the cause remains unidentified.

Radial nerve neuropathy (supinator syndrome; tunnel syndrome at the level of the spiral canal of the shoulder) is rarely accompanied by noticeable atrophy. Compression of the radial nerve in the spiral canal usually develops with a humeral fracture. Sensory disturbances are often absent. Localized pain in the compression zone is typical. A "drooping or falling wrist" is characteristic. Hypotrophy of the muscles of the back of the shoulder and forearm may be detected. Supinator syndrome is characterized by pain along the dorsal surface of the forearm, wrist and hand; weakness of forearm supination, weakness of the extensors of the main phalanges of the fingers and paresis of abduction of the first finger are observed.

Scalene muscle syndrome with compression of the upper or lower part of the vascular-nerve bundle (a variant of plexopathy) may be accompanied by hypotrophy of the hypothenar and, partially, thenar muscles. The primary trunk of the plexus between the anterior and middle scalene muscles and the underlying 1 rib is compressed. Pain and paresthesia are observed in the neck, shoulder girdle, shoulder, and along the ulnar edge of the forearm and hand. Pain is characteristic at night and during the day. It intensifies with a deep breath, when turning the head to the affected side and when tilting the head to the healthy side, and when abducting the arm. Edema and puffiness are observed in the supraclavicular region; pain is felt upon palpation of the tense anterior scalene muscle. A weakening (or disappearance) of the pulse on the a. radialis of the affected arm is characteristic when turning the head and taking a deep breath.

Pectoralis minor syndrome can also cause compression of the brachial plexus (a variant of plexopathy) under the tendon of the pectoralis minor muscle (hyperabduction syndrome). There is pain along the anterior upper surface of the chest and in the arm; weakening of the pulse when placing the arm behind the head. Pain on palpation of the pectoralis minor muscle. There may be motor, autonomic and trophic disorders. Severe atrophy is rare.

The superior thoracic outlet syndrome is manifested by plexopathy (compression of the brachial plexus in the space between the first rib and the clavicle) and is characterized by weakness of the muscles innervated by the lower trunk of the brachial plexus, i.e. the fibers of the median and ulnar nerves. The function of flexion of the fingers and wrist suffers, which leads to a gross impairment of function. Hypotrophy in this syndrome develops in the late stages mainly in the hypothenar region. Pain is usually localized along the ulnar edge of the hand and forearm, but can be felt in the proximal parts and chest. The pain intensifies when tilting the head to the side opposite to the tense scalene muscle. The subclavian artery is often involved (weakening or disappearance of the pulse with maximum rotation of the head in the opposite direction). A characteristic swelling is revealed in the supraclavicular fossa, compression of which intensifies pain in the arm. The brachial plexus trunk is most often pinched between the 1st rib and the clavicle (thoracic outlet). The superior aperture syndrome can be purely vascular, purely neuropathic, or, less commonly, mixed.

Predisposing factors: cervical rib, hypertrophy of the transverse process of the seventh cervical vertebra, hypertrophy of the anterior scalene muscle, deformation of the clavicle.

Plexopathy. The length of the brachial plexus is 15-20 cm. Depending on the cause, syndromes of total or partial damage to the brachial plexus may be observed. Damage to the fifth and sixth cervical roots (C5 - C6) or the upper primary trunk of the brachial plexus manifests itself as Duchenne-Erb palsy. Pain and sensory disturbances are observed in the proximal parts (supraglon, neck, scapula and in the deltoid muscle area). Paralysis and atrophy of the proximal muscles of the arm (deltoid, biceps brachii, anterior brachialis, pectoralis major, supraspinatus and infraspinatus, subscapularis, rhomboid, anterior serratus and others) are characteristic, but not the muscles of the hand.

Damage to the eighth cervical and first thoracic roots or the lower trunk of the brachial plexus results in Dejerine-Klumpke paralysis. Paresis and atrophy of the muscles innervated by the median and ulnar nerves develop, primarily the muscles of the hand, with the exception of those innervated by the radial nerve. Sensory disturbances are also observed in the distal parts of the arm.

An additional cervical rib must be excluded.

There is also a syndrome of isolated damage of the middle part of the brachial plexus, but it is rare and is manifested by a defect in the zone of proximal innervation of the radial nerve with preserved function of m. brachioradialis, which is innervated from the roots C7 and C6. Sensory disturbances can be observed on the back of the forearm or in the zone of innervation of the radial nerve on the back of the hand, but they are usually expressed minimally. In fact, this syndrome is not accompanied by atrophy of the hand muscles.

The above plexopathic syndromes are characteristic of lesions of the supraclavicular part of the brachial plexus (pars supraclavicularis). When the infraclavicular part of the plexus is affected (pars infraclavicularis), three syndromes are observed: the posterior type (lesion of the fibers of the axillary and radial nerves); the lateral type (lesion of the n. musculocutaneus and the lateral part of the median nerve) and the middle type (weakness of the muscles innervated by the ulnar nerve and the medial part of the median nerve, which leads to severe dysfunction of the hand).

Causes: trauma (most common), including birth and backpack trauma; radiation exposure (iatrogenic); tumors; infectious and toxic processes; Parsonage-Turner syndrome; hereditary plexopathy. Brachial plexopathy, apparently of dysimmune origin, has been described in the treatment of spasmodic torticollis with botulinum toxin.

Pancoast syndrome is a malignant tumor of the apex of the lung with infiltration of the cervical sympathetic chain and brachial plexus, manifested more often in adulthood by Horner's syndrome, difficult to localize causalgic pain in the shoulder, chest and arm (usually along the ulnar edge) with subsequent addition of sensory and motor manifestations. Characteristic is the limitation of active movements and atrophy of the arm muscles with loss of sensitivity and paresthesia.

Lateral amyotrophic sclerosis manifests itself in unilateral amyotrophy at the onset of the disease. If the process begins in the distal parts of the hand (the most common variant of disease development), then its clinical marker is such an unusual combination of symptoms as unilateral or asymmetric amyotrophy (more often in the thenar area) with hyperreflexia. In advanced stages, the process becomes symmetrical.

Complex regional pain syndrome type I (without peripheral nerve damage) and type II (with peripheral nerve damage). Obsolete names: "shoulder-hand" syndrome, "reflex sympathetic dystrophy". The syndrome is characterized mainly by a typical pain syndrome developing after injury or immobilization of the limb (after several days or weeks) in the form of poorly localized boring extremely unpleasant pain with hyperalgesia and allodynia, as well as local vegetative-trophic disorders (edema, vasomotor and sudomotor disorders) with osteoporosis of the underlying bone tissue. Mild atrophic changes in the skin and muscles in the affected area are possible. Diagnosis is made clinically; there are no special diagnostic tests.

A spinal cord tumor, especially an intracerebral one, when located in the area of the anterior horn of the spinal cord, can give local hypotrophy in the area of the hand muscles as the first symptom, followed by the addition and steady increase of segmental paretic, hypotrophic and sensory disorders, to which are added symptoms of compression of the long conductors of the spinal cord and the cerebrospinal fluid space.

Syringomyelia at the onset of the disease can manifest itself not only as bilateral hypotrophy (and pain), but sometimes as unilateral symptoms in the hand area, which, as the disease progresses, become bilateral in nature with the addition of other typical symptoms (hyperreflexia in the legs, trophic and characteristic sensory disturbances).

Hemiparkinsonism-hemiatrophy syndrome is a rare disease with unusual manifestations in the form of relatively early-onset (34-44 years) hemiparkinsonism, which is often combined with symptoms of dystonia on the same side of the body and "hemiatrophy of the body", which is understood as its asymmetry, usually in the form of a decrease in the size of the hand and foot, less often - the trunk and face on the side of neurological symptoms. Asymmetry of the hands and feet is usually noticed in childhood and does not affect the motor activity of the patient. CT or MRI of the brain in about half of the cases reveals an enlargement of the lateral ventricle and cortical grooves of the cerebral hemispheres on the side opposite to hemiparkinsonism (less often, the atrophic process in the brain is detected on both sides). The cause of the syndrome is considered to be hypoxic-ischemic perinatal brain injury. The effect of levodopa is noted only in some patients.

II. Bilateral atrophy of the muscles of the hand

Motor neuron disease (ALS) at the stage of advanced clinical manifestations is characterized by bilateral atrophy with hyperreflexia, other clinical signs of damage to the motor neurons of the spinal cord (paresis, fasciculations) and (or) the brainstem and corticospinal and corticobulbar tracts, a progressive course, as well as a characteristic EMG picture, including in clinically intact muscles.

Progressive spinal amyotrophy at all stages of the disease is characterized by symmetrical amyotrophy, absence of symptoms of pyramidal tract involvement and other brain systems in the presence of EMG signs of damage to motor neurons of the anterior horns of the spinal cord (motor neuronopathy) and a relatively favorable course. Most forms of progressive spinal amyotrophy (PSA) affect mainly the legs, but there is a rare variant (type V distal PSA) with predominant damage to the upper limbs ("Aran-Duchenne hand").

Hereditary distal myopathy has similar clinical manifestations, but without clinical and EMG manifestations of anterior horn involvement. A family history is usually present. EMG and muscle biopsy indicate the muscle level of involvement.

Plexopathy (rare) shoulder can be bilateral and total with some traumatic effects (crutch injury, etc.), an additional rib. A picture of bilateral flaccid paresis with limitation of active movements, diffuse atrophy including in the area of the hands and bilateral sensory disorders is possible.

With superior aperture syndrome, the “drooping shoulders” syndrome has been described (more often in women with a characteristic constitution).

Polyneuropathy with predominant damage to the upper limbs is typical for lead intoxication, acrylamide, skin contact with mercury, hypoglycemia, porphyria (the hands are affected first and mainly in the proximal parts).

Syringomyelia in the area of the cervical thickening of the spinal cord, if it is predominantly anterior corneal, manifests itself as bilateral atrophy of the hand muscles and other symptoms of flaccid paresis in the arms, dissociated segmental sensory disturbances and, as a rule, pyramidal insufficiency in the legs. MRI confirms the diagnosis.

Carpal tunnel syndrome can often be observed on both sides (occupational trauma, endocrinopathies). In this case, atrophy in the innervation zone of the median nerve will be bilateral, more often - asymmetrical. In these cases, it is necessary to conduct a differential diagnosis with polyneuropathy.

Spinal cord injury at the stage of residual effects may manifest itself as a picture of complete or partial damage (rupture) of the spinal cord with the formation of cavities, scars, atrophy and adhesions with a wide variety of symptoms, including atrophy, flaccid and central paralysis, sensory and pelvic disorders. Anamnesis data usually do not give reason for diagnostic doubts.

Spinal cord tumor. Intramedullary primary or metastatic tumors affecting the anterior horns of the spinal cord (ventrally located) cause atrophic paralysis along with symptoms of compression of the lateral columns of the spinal cord with conductive sensory and motor symptoms. Progressive segmental and conductive disorders with dysfunction of the pelvic organs, as well as CT or MRI data help to make the correct diagnosis.

Differential diagnosis in such cases is often carried out primarily with syringomyelia.

A rather rare syndrome is congenital isolated thenar hypoplasia, which is unilateral in most cases, but bilateral cases have been described. Sometimes it is accompanied by developmental anomalies of the bones of the thumb. Most of the described observations were sporadic.

Diagnostic tests for hand muscle atrophy

Complete blood count and biochemistry; urine analysis; serum muscle enzyme activity (mainly CPK); urine creatine and creatinine; EMG; nerve conduction velocity; muscle biopsy; chest and cervical spine X-ray; CT or MRI of the brain and cervicothoracic spine.

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