CHAPTER 29

Muscle Volume and Contour

A search for evidence of muscle atrophy or hypertrophy is an important part of the motor examination. There is normally an appreciable individual variation in muscular development, but noteworthy changes in the size or shape of individual muscles or muscle groups, especially when focal or asymmetric, may be significant.

Muscle atrophy (amyotrophy) causes a decrease in muscle volume or bulk and is usually accompanied by changes in shape or contour. Neurologic conditions likely to cause muscle atrophy are primarily those that affect the following components of the motor unit: the anterior horn cell, the nerve root(s), the peripheral nerve, or the muscle. Neuromuscular junction disorders do not cause muscle atrophy. Atrophy may also result from such things as disuse or inactivity, immobilization, tendonotomy, muscle ischemia, malnutrition, endocrine disorders, and normal aging.

Muscle hypertrophy is an increase in the bulk, or volume, of muscle tissues. It may result from excessive use of the muscles (physiologic hypertrophy) or occur on a pathologic basis. Hypertrophied muscle is not necessarily stronger than normal. Persistent abnormal muscle contraction may cause hypertrophy. Patients with myotonia congenita have a diffuse muscularity without significant increase in strength. Patients with dystonia may develop hypertrophy of the abnormally active muscle. In cervical dystonia (spasmodic torticollis), it is common to see hypertrophy of one sternomastoid muscle. Muscular dystrophies, especially Duchenne’s dystrophy, often cause pseudohypertrophy of muscle, with enlargement because of infiltration of the muscle with fat and connective tissue without an actual increase in muscle fiber size or number.

Examination of Muscle Volume and Contour

There is a great deal of individual variation in muscular development, in part constitutional and in part because of training, activity, and occupation. Certain individuals have small or poorly developed muscles, whereas others show outstanding muscular development. The sedentary, the elderly, and those with chronic disease may have small muscles without evidence of wasting or atrophy. Athletes may develop physiologically hypertrophic muscles. In normal individuals, the dominant side may exhibit an increase in the size of the muscles, even of the hand and foot. The appraisal of bulk and contour should be correlated with the other parts of the motor examination, especially with the evaluation of strength and tone.

Muscle volume and contour may be appraised by inspection, palpation, and measurement. Inspection generally compares symmetric parts on the two sides of the body, noting any flattening, hollowing, or bulging of the muscle masses. The muscles of the face, shoulder, and pelvic girdles, and distal parts of the extremities—especially the palmar surfaces of the hands, the thenar and hypothenar eminences, and the interosseous muscles—should be examined specifically. A useful technique for comparing extremities is to look down the long axis. Hold the patient’s arms outstretched and close together, comparing “down the barrel” from fingertips to shoulders for any asymmetry.

Palpation assesses muscle bulk, contour, and consistency. Normal muscles are semielastic and regain their shape at once when compressed. When hypertrophy is present, the muscles are firm and hard; in pseudohypertrophy, they appear enlarged but may feel doughy or rubbery on palpation. The feel of pseudohypertrophy has been likened to that of a plastic, gelatinous toy such as an imitation snake. Atrophic muscles are often soft and pulpy in consistency. When degenerated muscles have undergone fibrotic changes, they may feel hard and firm. Those infiltrated or replaced by fat may feel pliant and flabby.

Measurements may be very useful in assessing atrophy or hypertrophy. A pronounced difference in muscle size may be recognized at a glance, especially when confined to one side of the body, one extremity, or one segment of a limb. Slight differences are more difficult to detect, and measurements with a tape measure or calipers may be necessary. Measurements should be made from fixed points or landmarks and the sites—such as the distance above or below the olecranon, anterior superior iliac spine, or patella—recorded. The extremities should be in the same position and in comparable states of relaxation. It may also be valuable to measure the length of the limbs.

Atrophy or hypertrophy may be limited to an individual muscle, to muscles supplied by a specific structure (e.g., a nerve or root), to those muscles supplied by certain spinal cord segments, or to one-half of the body; or it may be multifocal or generalized. In atrophy related to arthritis and disuse, there may be a pronounced decrease in volume with little change in strength. In myopathies, on the other hand, there is often little atrophy in spite of a striking loss of power. Examination of the skin and subcutaneous tissues may also be relevant, especially in such conditions as dermatomyositis.

Abnormalities of Volume and Contour

Muscular Atrophy

Many processes may cause muscular atrophy. Neurogenic atrophy follows disease of the anterior horn cell, root, or peripheral nerve. Atrophy because of other neurologic processes, such as the hemiatrophy associated with congenital hemiplegia, is not typically considered neurogenic atrophy even though it is related to nervous system disease. The term neurogenic atrophy as commonly used implies disease affecting some part of the lower motor neuron. Myogenic atrophy is that due to muscle disease, such as muscular dystrophy. As a generalization, when weakness and wasting are comparable, the process is more likely to be neurogenic; when the weakness is disproportionately greater than the wasting, the process is more likely to be myopathic. When a muscle appears wasted but is not weak, the cause is likely to be nonneurologic, such as disuse.

Neurogenic Atrophy

The anterior horn cell and its processes exert a trophic effect on skeletal muscle. The nature of the trophic effect remains poorly understood, but it is not as simple as the effect of nerve impulses. Electrical stimulation of the peripheral nerve, sometimes done after peripheral nerve injury or Bell’s palsy, does not help prevent or reverse neurogenic atrophy. Nerves may be involved in regulating the trophic actions of insulin-like growth factor, calcitonin gene–related peptide, and other neurotrophic factors that have an influence on skeletal muscle. When a lesion completely disrupts the lower motor neuron or its peripheral processes, the affected muscle lies inert and flaccid and no longer contracts voluntarily or reflexively. Muscle fibers decrease in size, causing wasting or atrophy of the entire muscle mass. Without timely reinnervation, the muscle may become fibrotic, with an increase in connective tissue and fatty infiltration.

The more abrupt or extreme the interruption of nerve supply, the more rapid the wasting. The atrophy may either precede or follow other signs, such as weakness. In rapidly progressing diseases, weakness precedes atrophy, but in slowly progressive diseases, the atrophy may precede appreciation of weakness. If the pathologic process is confined to the anterior horn cells or the spinal cord, the neurogenic atrophy is segmental in distribution. Some conditions cause rapid destruction of the anterior horn cells and atrophy in the distribution of the affected spinal cord segments that develops within a short period of time (e.g., poliomyelitis).

In more slowly progressive disorders of the motor neuron (e.g., amyotrophic lateral sclerosis [ALS]), there is a gradual but widespread degeneration of the brainstem motor nuclei and anterior horn cells, causing progressive muscular atrophy that may appear before paralysis is evident (Figure 29.1). The distribution of the atrophy is important. To make a diagnosis of motor neuron disease, it is necessary to demonstrate widespread denervation in a multiple nerve, multiple root distribution. Eventually, the disease becomes widespread, but it often begins segmentally in one limb. Rarely, it may remain confined to one limb (monomelic motor neuron disease, Hirayama disease, O’Sullivan-McLeod syndrome). Particular groups of muscles are often affected. In classical ALS and in progressive spinal muscular atrophy (SMA) of the Aran-Duchenne type, atrophy is usually first seen in the distal musculature—the thenar, hypothenar, and interosseous muscles of the hand and the small muscles of the foot—and then spreads up the limbs to the proximal parts. In some patients, ALS seems to have a tendency to preferentially involve the muscles of the lateral half of the hand, median-innervated thenar, and ulnar-innervated first dorsal interosseous muscles while sparing the hypothenar muscles (split hand syndrome). Although not common, this pattern seems to be relatively specific for anterior horn cell disorders. In progressive bulbar palsy, the atrophy is first noted in the muscles supplied by the 12th, 10th, and 7th cranial nerves. In hereditary motor neuron syndromes, the involvement is often proximal. In SMA type 1 (infantile progressive SMA, Werdnig-Hoffmann disease), the atrophy first involves the trunk, pelvic, and shoulder muscles and then spreads toward the periphery. The proximal distribution and slow progression in SMA type 3 (juvenile proximal SMA, Kugelberg-Welander disease) may simulate muscular dystrophy. Segmental atrophy may also follow focal spinal cord lesions involving the anterior horn cells (e.g., syringomyelia). The rapidity of the progress depends upon the type of pathologic change.

FIGURE 29.1 A patient with amyotrophic lateral sclerosis showing advanced atrophy of the muscles of the shoulder girdle and upper arms (A) and intrinsic hand muscles (B).

Involvement of nerve roots, plexus elements, or peripheral nerves leads to atrophy of the muscles supplied by the diseased or injured component (Figure 29.2). With severe lesions involving a peripheral nerve or nerve plexus, atrophy may develop within a short period of time. Within 1 month after denervation, there may be a 30% loss of weight in the affected muscle and a 50% loss within 2 months; thereafter, the atrophy progresses more slowly and replacement by connective tissue and infiltration by fat follows. Lesions involving single nerve roots usually do not cause much atrophy, because most muscles are innervated from more than one level. Marked wasting in a disease that appears consistent with radiculopathy suggests multiple root involvement. In generalized peripheral neuropathy, weakness and wasting are usually greatest in the distal portions of the extremities. The amount of atrophy depends on the severity and chronicity of the neuropathy. The hereditary peripheral neuropathy, Charcot-Marie-Tooth disease (peroneal muscular atrophy), typically causes marked atrophy in a characteristic distribution involving the lower legs (inverted champagne bottle deformity; Figure 29.3).

FIGURE 29.2 Atrophy of the left abductor pollicis brevis in a plumber with carpal tunnel syndrome.

FIGURE 29.3 A patient with type 1 Charcot-Marie-Tooth disease. Despite a muscular upper body, there is marked atrophy of the lower extremities below the knees.

The complete syndrome of peripheral nerve dysfunction, with paralysis, atrophy, sensory impairment, areflexia, and trophic changes in the skin and other tissues, is the result of interruption of motor, sensory, and autonomic fibers. Interruption of sensory nerve fibers alone does not lead to muscular atrophy except as related to disuse, but loss of pain sensation may predispose one to painless injuries, including ulcerations following minor trauma and burns. The autonomic system is involved in trophic function by regulating the nutrition and metabolism of muscle and other tissues. Because of interruption of autonomic pathways, diseases of the lower motor neuron may be associated with trophic changes in the skin and subcutaneous tissues: edema, cyanosis or pallor, coldness, sweating, changes in the hair and nails, alterations in the texture of the skin, osteoporosis, and even ulcerations and decubiti. Autonomic fibers may be a factor in muscle atrophy because of “trophic dysfunction” and loss of vasomotor control.

Upper motor neuron lesions in adults are usually not followed by atrophy of the paralyzed muscles except for some generalized loss of muscle volume and secondary wasting because of disuse, which is seldom severe. With lesions dating from birth or early childhood, there may be a failure of growth of the contralateral body (Figure 25.5). Such congenital hemiatrophy may involve one side of the face or the face and corresponding half of the body; it is characterized by underdevelopment not only of the muscles but also of the skin, hair, subcutaneous tissues, connective tissue, cartilage, and bone. Congenital hemihypertrophy is rarer than the corresponding hemiatrophy, and there are usually other anomalies. There may be underdevelopment of one-half of the body because of either lack of development or atrophy of the opposite cerebral hemisphere (cerebral hemiatrophy). Severe cerebral insults in early life may lead to hemiplegia, hemiatrophy, partial or hemiseizures, and the development of delayed hemidystonia (“4-hemi” syndrome). Experimentally, lesions of the motor cortex and the descending corticospinal pathways may be followed by muscular atrophy, and on occasion, severe wasting appears with cerebral hemiplegias. Usually, there are associated trophic and sensory changes, and the wasting may in part be secondary to involvement of the postcentral gyrus or parietal lobe, lesions of which are known to be followed by contralateral atrophy. The loss of muscle bulk associated with lesions of the parietal lobe may appear promptly; the degree of atrophy depends upon the size and character of the lesion and the extent of the hypotonia and sensory change. The distribution is determined by the localization of the process within the parietal lobe. It is most severe if the motor cortex or pathways are involved along with the sensory areas of the brain. Hemiatrophy may also complicate hemiparkinsonism. Rarely, hemiatrophy is idiopathic.

Other Varieties of Muscular Atrophy

Myogenic, or myopathic, atrophy occurs as a result of primary muscle disease. In some conditions, there may be prominent wasting without much weakness. In most of these, the primary pathologic change is type 2 fiber atrophy. Wasting with little weakness occurs in disuse, aging, cachexia, and some endocrine myopathies. Weakness out of proportion to wasting occurs in inflammatory myopathy, myasthenia gravis, and periodic paralysis.

Muscle wasting is common in muscular dystrophy, and the distribution of the wasting parallels the weakness. In dystrophinopathies, the weakness and atrophy primarily involve the pelvic and shoulder girdle muscles (Figure 29.4). Weakness of the hip and spine extensors causes difficulty in assuming the erect position, and the patient “climbs up his thighs” (Gowers’ sign or maneuver) in order to stand (Video Link 29.1). As the disease progresses, there is increasing wasting of all muscles of the shoulders, upper arms, pelvis, and thighs. In the face of all of the atrophy, certain muscles—particularly the calf muscles—are paradoxically enlarged because of pseudohypertrophy (see below). The limb-girdle syndromes also primarily involve the pelvic and shoulder girdles. In facioscapulohumeral (FSH) (Landouzy-Dejerine) dystrophy, the atrophy predominates in the muscles of the face, shoulder girdles (especially the trapezius and periscapular muscles), and upper arms, especially the biceps (Figure 29.5). Involvement is often asymmetric, and occasionally, there is pseudohypertrophy of the deltoid and other shoulder muscles.

FIGURE 29.4 A boy with Duchenne’s muscular dystrophy, showing wasting of the musculature in the shoulders and thighs; weakness and atrophy of the glutei cause difficulty in assuming the erect position, and the patient “climbs up on his thighs” (Gowers’ maneuver) in order to stand erect.

FIGURE 29.5 A patient with facioscapulohumeral muscular dystrophy showing atrophy of the muscles of the shoulders and upper arms and pronounced scapular winging.

Distal myopathies, affecting the muscles of the hands and feet, are occasionally seen. Wasting involving the distal extremities, with relative sparing of the hands and feet, is likely to be myopathic. In contrast, denervation atrophy involves the entire distal extremity, including the hand or foot. Some myopathies cause striking weakness and atrophy involving certain muscles or muscle groups. In myotonic dystrophy, there is prominent atrophy of the sternocleidomastoid muscles. Scapuloperoneal syndromes involve the periscapular and peroneal muscles. Selective involvement of the quadriceps occurs in inclusion body myositis and type 2B limb-girdle muscular dystrophy (dysferlin deficiency). Some myopathies have a curious tendency to affect certain muscles while sparing nearby muscle groups. FSH characteristically causes wasting of the biceps and triceps with sparing of the deltoid and forearm musculature creating the “Popeye” arm appearance (Figure 29.6). The diamond on quadriceps sign refers to asymmetric diamond-shaped bulges seen in the anterolateral thighs of patients with dysferlinopathy (LGMD 2B and Miyoshi myopathy) when standing with the knees slightly bent. Proximal and distal atrophy causes the curious island of sparing to stand out. Other unusual muscle shapes have been described as a manifestation of dysferlinopathy, such as selective biceps atrophy causing a “bowl-shaped biceps.”

FIGURE 29.6 The Popeye arm appearance in FSH dystrophy.

Disuse atrophy follows prolonged immobilization of a part of the body. It may be rapid in onset and can sometimes simulate neurogenic atrophy. Disuse atrophy may occur in an extremity after immobilization, such as casting, one that cannot be moved normally because of joint disease, such as arthritis, paresis following a cerebral lesion, or after prolonged bed rest. The quadriceps femoris is particularly susceptible to disuse atrophy because of bed rest or because of pain in the knee or hip. The degree of muscle wasting is greater than the degree of weakness, which may be minimal or absent. Muscle biopsy shows atrophy of type 2 fibers, with the earliest changes in the type 2B fibers. Disuse atrophy can occasionally occur in extremities that are not used because of nonorganic paralysis.

Arthrogenic atrophy may appear in association with joint disease. It is more severe and develops more rapidly in acute arthritis. Both rheumatoid arthritis and osteoarthritis may cause periarticular atrophy, with loss of muscle bulk around involved joints. Periarticular muscle atrophy may be particularly prominent in patients with HIV-associated arthritis. Atrophy of this type may in part be the result of inactivity or disuse, but other factors are likely involved.

Muscle atrophy may accompany malnutrition, weight loss, cachexia, and other wasting diseases. The loss of muscle mass is typically greater than the degree of accompanying weakness. A normal blood supply is essential to the nutrition and oxygenation of muscles, and ischemia may lead to muscle atrophy as well as to alterations in the skin and other trophic changes. In Volkmann ischemic contracture, atrophy accompanies the muscle shortening.

Endocrine dysfunction of various types may lead to atrophy and other changes in muscle. In thyrotoxic myopathy, atrophy is particularly prone to involve the shoulder girdle and may lead to scapular winging. Coarse fasciculations are often seen in the affected areas. With primary hyperparathyroidism, weakness may be associated with atrophy, hyperreflexia, and fasciculations simulating ALS (Vical’s syndrome). Myopathy because of excess corticosteroids, exogenous or endogenous, may be associated with muscle wasting. Muscular weakness and atrophy are also frequent findings in hypopituitarism because of loss of thyroid and adrenal cortical hormones. Muscle wasting also occurs with diabetes. Distal weakness and atrophy are common in diabetic distal axonopathy. Diabetic amyotrophy (or radiculoplexus neuropathy) is a common syndrome of bilateral but asymmetric weakness and atrophy that involves the pelvic and thigh muscles because of involvement of the lumbosacral plexus and nerve roots. It is usually associated with severe pain. Patients with diabetes may also develop either localized lipoatrophy or areas of focal muscular atrophy because of repeated injections of insulin in the same area. The loss of subcutaneous tissue may simulate muscle atrophy. In adiposis dolorosa (Dercum’s disease), the muscles may be replaced with fat.

Congenital hypoplasia or absence of a muscle may be mistaken for atrophy. Almost any muscle may be congenitally absent, but some are particularly prone, including the depressor anguli oris, palmaris longus, trapezius, peroneus tertius, and anterior abdominal muscles (prune-belly syndrome). In the Holt-Oram syndrome, there are absent or hypoplastic thenar muscles. Poland syndrome is a rare anomaly characterized by unilateral absence of the pectoral muscles and ipsilateral hand abnormalities; it may be associated with a variety of other congenital anomalies. Other syndromes of congenital muscle abnormality include Duane retraction syndrome, Möbius’ syndrome, and congenital ptosis.

Muscular Hypertrophy and Pseudohypertrophy

Enlarged muscles are encountered less frequently than atrophy. In true muscle hypertrophy, the muscle is enlarged; in pseudohypertrophy, the muscle appears enlarged because it is replaced by fat and fibrous tissue. Extremely muscular individuals may show pronounced development of certain groups of muscles because of functional or physiologic hypertrophy, often found in athletes and heavy manual laborers. Microscopic examination shows an increase in the diameter of muscle fibers, primarily the type 2 fibers, without any increase in the number of fibers. Except for physiologic hypertrophy because of exercise, pseudohypertrophy is encountered more commonly than true hypertrophy.

Pseudohypertrophy is common in some forms of muscular dystrophy. Muscle biopsy reveals severe myopathy, with fatty and connective tissue infiltrations. Pseudohypertrophy is common in Duchenne’s and Becker’s dystrophy; an alternate term for Duchenne’s dystrophy is pseudohypertrophic muscular dystrophy. Certain muscles, particularly the calf muscles and the infraspinatus, are often strikingly enlarged because of pseudohypertrophy (Figure 29.7). Comparing the circumference of the calf to the knee is most informative. In the early stages of the disease, the enlarged muscles may feel firm and hard and remain strong, and there may actually be an element of true hypertrophy. With progression, they develop a soft doughy or rubbery feeling.

FIGURE 29.7 Pseudohypertrophy of the calves in Duchenne’s muscular dystrophy. (Reprinted from Schaaf CP, Zschocke J, Potocki L. Basiswissen Humangenetik. Heidelberg: Springer Midizin; 2008. Figure 31.11. Reproduced with permission of Springer in the format Book via Copyright Clearance Center.)

Muscle hypertrophy is common in myotonia congenita, especially the dominant form (Thomsen’s disease), because of the excessive contraction. These patients may have the impressive muscularity of a bodybuilder; although they may appear strong and muscular, strength is normal, or there is even slight weakness. Hypertrophia musculorum vera is a hereditary syndrome causing enlargement of the muscles, usually those of the limbs, but any area may be affected. Mutations in the myostatin gene may cause muscle hypertrophy.

Muscle enlargement, either true hypertrophy or pseudohypertrophy, occurs as an occasional feature in other neuromuscular disorders, including Kugelberg-Welander disease, central core disease, centronuclear myopathy, autosomal recessive limb-girdle muscular dystrophy, acid maltase deficiency, polymyositis, FSH muscular dystrophy, inclusion body myositis, hyperkalemic periodic paralysis, paramyotonia congenita, proximal myotonic myopathy, Isaac’s syndrome, focal myositis, and in manifesting dystrophinopathy carriers. Chronic partial denervation of muscle occasionally leads to focal muscle hypertrophy, presumably because of compensatory physiologic hypertrophy of unaffected fibers or parts of the muscle. Muscle hypertrophy has been reported as a manifestation of radiculopathy and rarely in other neurogenic processes. Use or abuse of androgenic steroids or beta-2 adrenergic agonists may lead to muscle hypertrophy.

Muscle enlargement may occur in hypothyroidism. The enlarged muscles have reduced strength, fatigability, and slowness of contraction and relaxation. The Kocher-Debré-Semelaigne (infant Hercules) syndrome is diffuse muscular hypertrophy because of hypothyroidism, particularly early in life. Hoffman syndrome refers to a hypertrophic myopathy because of hypothyroidism in adults. Early acromegaly may cause generalized muscular hypertrophy with increased strength, but in later stages, there is weakness and amyotrophy. Edema and inflammation of muscles may simulate hypertrophy. Muscle enlargement may also occur due to interstitial infiltrates, as occurs in cysticercosis, trichinosis, sarcoidosis, and amyloidosis. Focal muscle enlargement may occur with benign or malignant neoplasms. The masseters may become enlarged because of bruxism or as a familial condition.

Loss of body fat may lend the appearance of muscle enlargement. In the lipodystrophies, which may be familial and acquired, there is loss of adipose tissue that may be focal or generalized, often associated with metabolic complications, such as diabetes mellitus and hypertriglyceridemia. Köbberling-Dunnigan syndrome is a familial partial lipodystrophy that may result in an appearance of excessive muscularity, particularly in females.

Video Links

Video Link 29.1. Gowers’ sign. http://neurosigns.org/wiki/Gower%27s_sign

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