Proximal muscle weakness: causes, symptoms, diagnosis, treatment

Most of the diseases discussed here result in bilateral proximal weakness and atrophy of a symmetrical nature (with the exception of proximal diabetic polyneuropathy, neuralgic amyotrophy, and, to some extent, amyotrophic lateral sclerosis) in the arms and legs. Syndromes of the brachial and lumbosacral plexus (plexopathies), which are more often unilateral, are not discussed here.

Proximal muscle weakness may be seen predominantly in the arms, predominantly in the legs, or may develop in a generalized manner (in both arms and legs).

Predominantly in the arms, proximal muscle weakness may sometimes be a manifestation of amyotrophic lateral syndrome; some forms of myopathies (including inflammatory); early stages of Guillain-Barré syndrome; Parsonage-Turner syndrome (usually unilateral); polyneuropathy associated with hypoglycemia; amyloid polyneuropathy and some other forms of polyneuropathy.

Proximal muscle weakness predominantly in the legs can be caused by almost the same diseases; some forms of myopathy; polyneuropathy (diabetic, some toxic and metabolic forms), polymyositis, dermatomyositis, some forms of progressive spinal amyotrophy. Some of the listed diseases can simultaneously or sequentially cause proximal weakness in both arms and legs.

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The main causes of proximal muscle weakness are:

1. Myopathy (several variants).
2. Polymyositis (dermatomyositis).
3. Proximal diabetic polyneuropathy.
4. Neuralgic amyotrophy.
5. Myelitis.
6. Guillain-Barré syndrome and other polyneuropathies.
7. Amyotrophic lateral sclerosis.
8. Proximal forms of progressive spinal amyotrophy.
9. Paraneoplastic motor neuron disease.

Myopathy

With gradual development of bilateral proximal muscle weakness in the proximal parts of the limbs, myopathy should be considered first of all. The initial stage of the disease is characterized by muscle weakness, the degree of which significantly exceeds the slightly expressed atrophy of the corresponding muscles. Fasciculations are absent, deep reflexes from the limbs are preserved or slightly reduced. There are no changes in the sensory sphere. During physical exertion, the patient may experience pain, which indicates a fairly widespread involvement of the corresponding muscle groups in the pathological process and indicates a disruption in the functioning of the normal mechanism of alternately including the working and resting portion of the muscle (muscles).

The main clinical phenomenon can be clearly recorded in an electromyographic study: a characteristic sign is the early inclusion of a large number of muscle fibers, which is reflected in the form of a characteristic "dense" pattern of the motor unit action potential. Since in myopathy almost all muscle fibers of the affected muscle are involved in the pathological process, the amplitude of the motor unit action potential is significantly reduced.

Myopathy is not a diagnosis; the term only indicates the muscular level of damage. Not all myopathies are degenerative. Clarifying the nature of the myopathy allows for the development of appropriate treatment tactics. Some myopathies are manifestations of potentially curable diseases, such as metabolic disorders or autoimmune diseases.

Laboratory tests can provide quite valuable information about the possible cause of myopathy. The most informative is the study of muscle biopsy. In addition to the study of myobiopsy by light or electron microscopy, it is absolutely necessary to use modern enzymatic histochemical and immunochemical studies.

The first of the "degenerative" myopathies to be considered is muscular dystrophy. The most common clinical variant, manifested as proximal muscle weakness, is the "limb-girdle" form of muscular dystrophy. The first signs of the disease are usually detected in the 2nd decade of life; the disease is characterized by a relatively benign course. It manifests itself as muscle weakness, and then atrophy of the muscles of the pelvic girdle and proximal parts of the legs; less often, the muscles of the shoulder girdle are also affected simultaneously. The patient begins to use characteristic "myopathic" techniques in the process of self-care. A specific habitus with a "duck" gait, hyperlordosis, "winged shoulder blades" and characteristic dysbasia develops. Another form of muscular dystrophy is quite easily diagnosed - pseudohypertrophic Duchenne myodystrophia, which, on the contrary, is characterized by rapid progression and debut at the age of 5 to 6 years exclusively in boys. Becker muscular dystrophy is similar to Duchenne muscular dystrophy in the nature of muscle involvement, but is characterized by a benign course. The proximal parts of the arms are involved in the pathological process in facioscapulohumeral muscular dystrophy.

At the top of the list of non-degenerative myopathy (which, of course, is not complete here and is presented only by the main forms) should be chronic thyrotoxic myopathy (and other endocrine myopathies). In general, any endocrine pathology can lead to the development of chronic myopathy. A feature of myopathy in systemic lupus erythematosus is painful muscle contractions. Paraneoplastic myopathy often precedes the appearance of symptoms of a malignant neoplasm. It is necessary to remember the possibility of developing iatrogenic steroid myopathy with proximal weakness (in the legs). The diagnosis of "menopausal myopathy" should be made only after excluding all other causes of myopathy. Myopathy in glycogen metabolism disorders develops mainly in childhood and is characterized by muscle pain during physical exertion. In general, the combination of proximal muscle weakness with pain on exertion should always alert the physician to possible underlying metabolic disturbances and should prompt laboratory testing and muscle biopsy.

Polymyositis

In most cases, the term "polymyositis" refers to an autoimmune disease that occurs with predominant involvement of the muscles of the proximal extremities and the muscles of the pelvic girdle (and neck muscles). The age and nature of the onset of the disease are highly variable. More typical is a gradual onset and course with relapses and periodic increase in symptoms, early onset of swallowing disorders, soreness of the affected muscles and laboratory data confirming the presence of an acute inflammatory process. Tendon reflexes are preserved. As a rule, the level of creatine phosphokinase in the blood is elevated, indicating rapid destruction of muscle fibers. Myoglobinuria is possible, while obstruction of the renal tubules with myoglobin can lead to the development of acute renal failure (as in the "compression" syndrome, "crush syndrome"). The presence of erythema on the face and chest ("dermatomyositis") helps in making a diagnosis. In men, polymyositis is often paraneoplastic.

EMG reveals the "myopathic changes" described above and spontaneous activity suggesting damage to the terminal branches of the nerves. In the acute stage of the disease, biopsy almost always confirms the diagnosis if the biopsy reveals perivascular infiltration with lymphocytes and plasma cells. However, in the chronic stage, polymyositis may be difficult to differentiate from muscular dystrophy.

Inflammatory processes in muscles caused by specific microorganisms stand apart from the main group of polymyositis. An example is viral myositis, characterized by an acute onset with severe pain and very high ESR. Severe pain is also typical of limited myositis in sarcoidosis and trichinosis. This is also typical of rheumatic polymyalgia (polymyalgia rheumatica) - a muscle disease that occurs in adulthood and old age and occurs with severe pain syndrome. True muscle weakness is usually absent or expressed minimally - movements are difficult due to intense pain, especially in the muscles of the shoulder and pelvic girdle. EMG and biopsy do not reveal signs of damage to muscle fibers. ESR is significantly elevated (50-100 mm per hour), laboratory indicators indicate a subacute inflammatory process, CPK is often normal. Mild anemia is possible. Corticosteroids have a rapid effect. Some patients subsequently develop cranial arteritis (temporal arteritis).

Proximal diabetic polyneuropathy (diabetic amyotrophy)

Proximal muscle weakness may be a manifestation of peripheral nervous system pathology, most often diabetic neuropathy. This clinical variant of diabetic polyneuropathy involving proximal muscle groups is much less known to physicians in contrast to the well-known form of diabetic polyneuropathy, which has a bilateral symmetrical distal sensorimotor defect. Some mature patients with diabetes develop proximal weakness in the limbs, usually asymmetrical, pain is often present, but the most obvious motor defect is weakness and proximal atrophy. Difficulty climbing up and down stairs, getting up from a sitting position, and moving from a supine position to a sitting position. Achilles reflexes may remain intact, but knee reflexes are usually absent; the quadriceps muscle of the thigh is painful on palpation, paretic and hypotrophic. Weakness is detected in m. ileopsoas. (A similar picture of asymmetric proximal weakness and atrophy is given by such diseases as carcinomatous or lymphomatous radiculopathy.)

For the development of proximal diabetic polyneuropathy (as well as for the development of all other forms of diabetic neuropathy), the presence of severe metabolic disorders is not at all necessary: sometimes they can be detected for the first time during a glucose tolerance test (latent diabetes).

Neuralgic amyotrophy (shoulder girdle; pelvic girdle)

Asymmetric proximal diabetic polyneuropathy in the lower extremities should be distinguished from unilateral lumbar plexus involvement, a disease similar to the well-known neuralgic amyotrophy of the shoulder girdle muscles. Clinical observations over the past 10 years have shown that a similar pathological process can also affect the lumbar plexus. The clinical picture is represented by symptoms of acute unilateral femoral nerve involvement with the development of paralysis of the muscles innervated by it. A thorough examination, including EMG and nerve conduction velocity testing, can also reveal mild involvement of adjacent nerves, such as the obturator nerve, which manifests itself as weakness of the adductor muscles of the thigh. The disease is benign, recovery occurs in a few weeks or months.

It is extremely important to make sure that the patient does not have two other possible diseases that require a specific diagnostic approach and treatment. The first is damage to the third or fourth lumbar spinal roots: in this case, sweating on the anterior surface of the upper thigh is not impaired, since the autonomic fibers leave the spinal cord in the roots no lower than the second lumbar.

Sweating is impaired by malignant neoplasms in the pelvis that affect the lumbar plexus, through which the autonomic fibers pass. Another cause of compression of the lumbar plexus that should be kept in mind is spontaneous retroperitoneal hematoma in patients receiving anticoagulants. In this situation, the patient experiences pain due to the initial compression of the femoral nerve by the hematoma; to relieve the pain, the patient takes analgesics, analgesics enhance the effect of anticoagulants, which leads to a further increase in the volume of the hematoma and pressure on the femoral nerve, followed by the development of paralysis.

Myelitis

Cases of myelitis with the development of proximal paresis have become rare since poliomyelitis has virtually disappeared from clinical practice. Other viral infections, such as those caused by Coxsackievirus type A, can mimic the poliomyelitis neurological syndrome, leading to the development of asymmetric proximal paresis with the absence of reflexes with preserved sensitivity. Increased cytosis, a slight increase in protein levels, and a relatively low lactate level are detected in the cerebrospinal fluid.

Guillain-Barré syndrome and other polyneuropathies

The myelitis described above should be differentiated from Guillain-Barré syndrome, which is a very difficult task in the first days of the disease. The neurological manifestations are very similar - even damage to the facial nerve can be observed in both diseases. Nerve conduction velocities in the first days may remain normal, the same applies to the protein level in the cerebrospinal fluid. Pleocytosis speaks in favor of myelitis, although it is also found in Guillain-Barré syndrome, in particular - in Guillain-Barré syndrome of viral origin (e.g., caused by the Epstein-Barr virus). Involvement of the autonomic nervous system is an important diagnostic criterion, testifying in favor of Guillain-Barré syndrome, if the areactivity of the heart rate to stimulation of the vagus nerve is proven or other symptoms of peripheral autonomic insufficiency are detected. Bladder dysfunction is observed in both pathological conditions, the same applies to paralysis of the respiratory muscles. Sometimes only observation of the course of the disease with repeated assessment of the neurological status and nerve conduction velocities allows a correct diagnosis to be made. Some other forms of polyneuropathy are also characterized by a predominantly proximal accentuation of the process (polyneuropathy during treatment with vincristine, with skin contact with mercury, polyneuropathy in giant cell arteritis). CIDP sometimes presents with a similar picture.

Amyotrophic lateral sclerosis

The debut of lateral amyotrophic sclerosis from the proximal parts of the hand is not a frequent phenomenon, but it is quite possible. Asymmetric amyotrophy (at the beginning of the disease) with hyperreflexia (and fasciculations) is a characteristic clinical marker of lateral amyotrophic sclerosis. EMG reveals anterior corneal involvement even in clinically intact muscles. The disease progresses steadily.

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Progressive spinal muscular atrophy

Some forms of progressive spinal amyotrophy (Werdnig-Hoffman amyotrophy, Kugelberg-Welander amyotrophy) are related to proximal spinal amyotrophies of hereditary nature. Fasciculations are not always present. Sphincter functions are preserved. EMG is of the utmost importance for diagnosis. Spinal cord conduction systems are usually not involved.

Paraneoplastic syndrome

Paraneoplastic motor neuron disease (spinal cord involvement) can sometimes mimic progressive spinal muscular atrophy.

How is proximal muscle weakness recognized?

General and biochemical blood tests; urine analysis; EMG; muscle biopsy; blood CPK level test; nerve conduction velocity test; cerebrospinal fluid test; therapist consultation; if necessary - oncologic screening and other (as indicated) tests.