Children with neuromuscular disorders commonly present with weakness, numbness, tingling, gait difficulty, or ataxia. Neurologists seek to elicit a detailed description of the symptoms and should not accept at face value all terminology used by patients or their parents. For example, patients may state that they feel “weak” when in fact their problem is stiffness, rigidity, or incoordination. Similarly, because some terms, such as “numbness” and “dizziness,” have a variety of meanings, neurologists will ask a patient reporting such symptoms to describe them in greater detail. One technique is to ask patients and their parents to describe tasks that might be impeded by the symptoms.

The time course of an illness often differentiates among etiologies. For example, trauma, infections, intoxications, and conversion reactions emerge acutely, over minutes to days. A subacute onset evolving over days to weeks typifies many systemic conditions, such as autoimmune, endocrine, and nutritional disorders. A chronic time course may suggest a genetic or metabolic abnormality. Because some conditions tend to progressively worsen while others are static, neurologists always try to determine if a patient’s symptoms are progressing or remaining stable. In addition, the patient’s age at the time the symptoms began should be ascertained, as many disorders have a typical age at onset.

As an example, consideration of the time course helps narrow the differential diagnosis of acute childhood paralysis. Hyperacute paralysis—developing over hours—is most often associated with hyperkalemia or hypokalemia or intoxication (such as with insecticides). It can also be psychogenic, perhaps triggered by an intolerable or disturbing thought or situation. In paralysis developing over days to weeks, Guillain-Barré syndrome (GBS) is the most common culprit. Other diagnoses to consider include transverse myelitis, botulism, MG, acute inflammatory diseases of muscle, infection of anterior horn cells by viruses (such as enteroviruses or, in endemic areas, polio), tick paralysis, and exposure to various neurotoxins. Rare causes include acute intermittent porphyria and diphtheria (1,2).

When approaching a patient with a possible neuromuscular disorder, neurologists attempt to identify comorbid medical conditions. Neuromuscular disorders may result from underlying medical illness, such as neuropathy due to leprosy, or from the treatment of medical illnesses, such as chemotherapy-induced neuropathy. Also, because some neuromuscular disorders involve other organs, evidence of such nonneurological involvement may serve as a clue to the diagnosis. Likewise, a single systemic illness may injure the PNS along with other systems. For example, MG may occur in conjunction with other autoimmune disorders.

Many substances of abuse, including alcohol, cocaine, and heroin, can damage the PNS. Glue sniffing, which is prevalent among adolescents, can cause neuropathy because users inhale toxic hexacarbons. Industrial exposures, to heavy metals for example, can also produce neuropathy.

Physicians should note birth complications, including prematurity and large birth weight (macrosomia). Particularly when evaluating a hypotonic (floppy) infant, they should attempt to determine if fetal movements were decreased during the third trimester, suggesting that weakness was present in utero.

Children with neuromuscular disorders may be delayed in attaining gross or fine motor milestones. On the other hand, coexisting impairment of language or other cognitive domains raises the likelihood of cerebral palsy or other brain pathology. Clinicians use instruments such as the Denver Developmental Screening Test (Denver Developmental Materials, Inc, Denver, CO) and its derivatives to assess whether children have achieved developmental milestones at the appropriate time and in the usual sequence.

Identifying an inherited disorder is critical for making an accurate diagnosis and providing genetic counseling. Physicians should ascertain whether family members are affected and, if so, attempt to determine the pattern of inheritance. Autosomal dominant conditions affecting the PNS include many types of hereditary neuropathy and certain myopathies, including myotonic dystrophy, facioscapulohumeral dystrophy, and one type of myotonia congenita. X-linked disorders include Duchenne and Becker muscular
dystrophies and several varieties of hereditary neuropathy. Exclusively maternal transmission suggests a mitochondrial disorder, such as mitochondrial encephalomyopathy, lactic acidosis, and stroke (MELAS) or myoclonic epilepsy and ragged-red fibers (MERFF). Even if a child has no obviously affected family member, parental consanguinity may suggest that the child has a genetic disorder with autosomal recessive inheritance.

Examination of the cranial nerves is described in detail in Chapter 1. Cranial nerves can be disrupted singly, in combination, or as part of a generalized polyneuropathy. Because most of the cranial nerves belong to the PNS, it is important to examine their function carefully in patients with suspected neuromuscular disease. In particular, the complaint of diplopia (double vision) often reflects weakness of eye movement (external ophthalmoparesis), which can result from damage to the oculomotor (CN III), trochlear (CN IV), and/or abducens (CN VI) nerves. Ptosis (drooping of the eyelid) uncommonly results from myopathy affecting muscles that elevate the eyelid; more often it is due to dysfunction of CN III or the sympathetic fibers that innervate those muscles or the NMJ that joins CN III to the muscles. Disturbance of facial sensation may reflect trigeminal nerve (CN V) dysfunction. Palsy of the facial nerve (CN VII) causes drooping of the face, such as in Bell’s palsy. Impaired auditory or vestibular function may suggest a lesion of the vestibulocochlear nerve (CN VIII). Difficulty speaking (dysarthria) and/or swallowing (dysphagia) can result from lesions affecting the glossopharyngeal (CN IX) or vagus (CN X) nerves. Neck flexion and turning and shoulder shrugging may be weak if the spinal accessory nerve (CN XI) is affected. With damage to the hypoglossal nerve (CN XII), the tongue may be weak or atrophic and fasciculations may be present.

When examining a patient, it is important for neurologists to remember that cranial nerve function depends not only on the cranial nerves themselves but also on related structures, such as the brainstem, NMJ, and cranial muscles. For example, external ophthalmoparesis can result not only from dysfunction of the oculomotor, trochlear, and/or abducens nerves but also from problems in the brainstem, NMJ, or extraocular muscles. Unilateral facial weakness usually signifies palsy of the facial nerve, but facial diparesis may result from neuropathy or myopathy.

The motor examination includes assessment of muscle bulk, tone, and power. Atrophy—loss of muscle bulk—characterizes disorders of the LMN. For example, the sequelae of a severe Erb’s palsy may include atrophy of the deltoid and biceps muscles due to injury to C5 and C6 nerve roots. Likewise, hammer toes, flat feet (pes planus), or high-arched feet (pes cavus) from atrophy of the foot muscles may bespeak hereditary or other long-standing motor neuropathy, especially in older children and adolescents. Atrophy may also result from prolonged disuse. On the other hand, hypertrophy of muscles may result from overuse, which may be intentional (as in bodybuilding) or a consequence of repetitive involuntary movements such as dystonia (see Chapter 3). Some conditions cause pseudohypertrophy, in which muscle fibers are unchanged in size but fatty infiltration or increased connective tissue enlarge the muscle bulk. A classic example is the calves of boys with Duchenne muscular dystrophy (DMD), which become enlarged by fibrosis of the muscle. Other examples include glycogen storage diseases and endocrine disorders such as hypothyroidism and acromegaly.

Neurologists assess muscle tone, another element of the motor examination, by moving the patient’s body parts through their range of motion and feeling for resistance. Decreased tone (hypotonia) is most closely associated with lesions of the LMN, but it also can occur with cerebral or cerebellar pathology. Increased muscle tone in children usually occurs in one of two forms. Spasticity is increased resistance to passive movement that is more pronounced when the movement is made quickly. In contrast, the resistance of rigidity does not change with varying speeds of movement. Spasticity is typical of damage to the UMN in the brain or spinal cord, while rigidity is most characteristic of disorders of the extrapyramidal system, most commonly the basal ganglia.

An important component of the motor examination is the assessment of power. In older children and adolescents, neurologists usually use manual muscle testing, in which the examiner asks the patient to contract a muscle group and grades the strength of the contraction along a 0 to 5 scale (Table 18.2). Children younger than 6 years often are unable to cooperate with formal testing, but even preschoolers may cooperate with requests to walk (including walking on heels and on toes), rise from a sitting position, or perform a deep knee bend. An astute examiner will glean a great deal of information simply by observing the patient.

Watching a child walk gives valuable information about muscle power as well other neurological functions (including vision, balance, and coordination). By the age of 13 to 18 months, most toddlers can walk steadily with only occasional falls. At 18 months, most children can stand unassisted from a sitting position. By 24 months, most children have mastered the skills of running and jumping (often to their parents’ dismay). Table 18.3 lists some patterns of gait abnormalities commonly observed in children.

Recognizing the pattern of motor involvement as more prominent either proximally or distally is crucial in identifying its underlying cause. Children with proximal muscle
weakness may have difficulty standing from a sitting position, and may need to use their hands to push on the floor and their knees, a maneuver known as Gowers sign (Fig. 18.1A-D,18.1E). A child with foot drop is likely to have trouble walking on his or her heels.

In general, muscle disease produces weakness and atrophy that is most pronounced proximally, while polyneuropathy results in predominantly distal abnormalities because it affects the longest nerves most severely. Exceptions include myotonic dystrophy, which is associated with distal weakness.

Examination of sensation is highly subjective and requires the cooperation of the patient. Young children may be unable to provide useful information on formal sensory testing, although dramatically different reactions to similar stimulation in discrete body parts may reflect differential sensation.

Lesions of the anterior horn cell, NMJ, and muscle do not result in sensory changes. In contrast, nerve and nerve root damage, as well as CNS pathology, can cause abnormalities in sensation. A major goal of the sensory examination is to identify an anatomic pattern of abnormalities because, in analogy with motor abnormalities, sensory changes can be very helpful in localizing the site of the lesion.

Testing sensation of stimuli in a variety of sensory modalities may demonstrate dissociation of sensory changes, such that some modalities are affected more than (or to the exclusion of) others. Testing multiple modalities can be helpful in localization, for, as mentioned previously, separate tracts in the spinal cord carry information about pain and temperature (spinothalamic tracts) and about vibration and joint position (dorsal columns). Although neurologists sometimes test sensation of light touch, pin prick, cold, hot, vibration, and joint position, performing such an exhaustive examination is rarely practical in young patients. Rather, the examiner must selectively test those modalities most likely to elicit information relevant to the individual patient.

Although disorders of the UMN typically produce hyperreflexia (overly brisk reflexes), diseases of the LMN tend to result in hyporeflexia or absent reflexes (areflexia). In length-dependent neuropathies, in which the longest nerves are preferentially damaged, a characteristic early sign is a bilaterally decreased Achilles tendon reflex. More focal reflex abnormalities occur in association with mononeuropathy, mononeuropathy multiplex, and radiculopathy Reflexes are largely spared in myopathies and NMJ disorders unless very severe weakness is present.

In most cases of ataxia in children, a CNS process is responsible. Nevertheless, PNS abnormalities that impair sensation of joint position can also result in ataxia. Most of these conditions are neuropathies that affect sensory fibers, either exclusively or together with motor fibers. A few conditions directly afflict the cell bodies of the sensory nerves, but these are rare, especially in children.