This chapter deals primarily with sensory disturbances of the limbs and trunk. Autonomic dysfunction is often associated with sensory loss but sometimes occurs alone. Chapter 17 considers sensory disturbances of the face.
Sensory Symptoms
Pain, dysesthesias, and loss of sensibility are the important symptoms of disturbed sensation. Peripheral neuropathy is the most common cause of disturbed sensation at any age. As a rule, hereditary neuropathies are more likely to cause loss of sensibility without discomfort, whereas acquired neuropathies are more likely to be painful. Discomfort is more likely than numbness to bring a patient to medical attention.
Nerve root pain generally follows a dermatomal distribution. Ordinarily, it is descripted as deep and aching. The pain is more proximal than distal and may be constant or intermittent. When intermittent, the pain may radiate in a dermatomal distribution. The most common cause of root pain in adults is sciatica associated with lumbar disk disease. Disk disease also occurs in adolescents, usually because of trauma. In children, radiculitis is a more common cause of root pain. Examples of radiculitis are the migratory aching of a limb preceding paralysis in the acute inflammatory demyelinating polyradiculoneuropathy/Guillain-Barré syndrome (see Chapter 7 ) and the radiating pain in a C5 distribution that heralds an idiopathic brachial neuritis (see Chapter 13 ).
Polyneuropathy involving small nerve fibers causes dysesthetic pain. This pain differs from previously experienced discomfort and the description is as pins and needles, tingling, or burning. It compares with the abnormal sensation felt when dental anesthesia is wearing off. The discomfort is superficial, distal, and usually symmetric. Dysesthetic pain is never a feature of hereditary neuropathies in children.
Loss of sensibility is the sole initial feature in children with sensory neuropathy. Because of the associated clumsiness, delay in establishing a correct diagnosis is common. Strength and tests of cerebellar function are normal and tendon reflexes are absent. The combination of areflexia and clumsiness should suggest a sensory neuropathy.
Table 9-1 summarizes the pattern of sensory loss as a guide to the anatomical site of abnormality and Box 9-1 a differential diagnosis of conditions with sensory deficits.
| Pattern | Site |
|---|---|
| All limbs | Spinal cord or peripheral nerve |
| Bothlegs | Spinal cord or peripheral nerve |
| Glove-and-stocking | Peripheral nerve |
| Legs and trunk | Spinal cord |
| One arm | Plexus |
| One leg | Plexus or spinal cord |
| Unilateral arm and leg | Brain or spinal cord |
B rachial N euritis
Neuralgic amyotrophy (see Chapter 13 )
Recurrent familial brachial neuropathy (see Chapter 13 )
C omplex R egional P ain S yndrome I ( Reflex S ympathetic D ystrophy )
C ongenital I nsensitivity (I ndifference ) to P ain
Lesch-Nyhan syndrome
Mental retardation
With normal nervous system
F oramen M agnum T umors
H ereditary M etabolic N europathies
Acute intermittent porphyria
Hereditary tyrosinemia
H ereditary S ensory and A utonomic N europathy (HSAN)
HSAN I (autosomal dominant)
HSAN II (autosomal recessive)
HSAN III (familial dysautonomia)
HSAN IV (with anhydrosis)
L umbar D isk H erniation
S yringomyelia
T halamic S yndromes
Painful Limb Syndromes
Three painful arm syndromes are acute idiopathic brachial neuritis (also called neuralgic amyotrophy or brachial plexitis), familial recurrent brachial neuritis, and complex regional pain syndrome (reflex sympathetic dystrophy). In the first two syndromes, muscle atrophy follows a transitory pain in the shoulder or arm. Monoplegia is the prominent feature (see Chapter 13 ). Although muscle atrophy also occurs in complex regional pain syndrome, pain is the prominent feature. Discussion of complex regional pain syndrome follows.
Complex Regional Pain Syndrome I
The presence of regional pain and sensory changes following a noxious event defines complex regional pain syndrome (CRPS). A working group of the International Association for the Study of Pain developed a new terminology that separates reflex sympathetic dystrophy (RSD) from causalgia ( ). CRPS I replaces the term RSD. The definition of CRPS I is defined as “a pain syndrome that develops after an injury, is not limited to the distribution of a single peripheral nerve, and is disproportional to the inciting event.” CRPS II requires demonstrable peripheral nerve injury and replaces the term causalgia.
Clinical Features
The essential feature of CRPS I is sustained burning pain in a limb combined with vasomotor and pseudomotor dysfunction, leading to atrophic changes in skin, muscle, and bone following trauma. The pain is of greater severity than that expected from the inciting injury. The mechanism remains a debated issue. Catecholamine hypersensitivity may account for the decreased sympathetic outflow and autonomic features in the affected limb ( ).
The mean age at onset in children is 11 years, and girls are more often affected than are boys. CRPS I frequently follows trauma to one limb, with or without fracture. The trauma may be relatively minor, and the clinical syndrome is so unusual that a diagnosis of “hysterical” or “malingering” is common. Time until onset after injury is usually within 1 or 2 months, but the average interval from injury to diagnosis is 1 year.
The first symptom is pain at the site of injury, which progresses either proximally or distally without regard for dermatomal distribution or anatomical landmarks. Generalized swelling and vasomotor disturbances of the limb occur in 80 % of children. Pain is intense, described as burning or aching, and is out of proportion to the injury. It may be maximally severe at onset or may become progressively worse for 3 to 6 months. Movement or dependence exacerbates the pain, causing the patient to hold the arm in a position of abduction and internal rotation, as if swaddled to the body. The hand becomes swollen and hyperesthetic and feels warmer than normal.
Children with CRPS I do better than do adults. Reported outcomes vary widely, probably based on the standard of diagnosis. In my own experience, most begin recovering within 6 to 12 months. Long-term pain is unusual, as are the trophic changes of the skin and bones that often occur in adults. Recovery is usually complete, and recurrence is unusual.
Diagnosis
The basis for diagnosis is the clinical features; laboratory tests are not confirmatory. Because the syndrome follows accidental or surgical trauma, litigation is commonplace, and requires careful documentation of the clinical features examination. In recent years, CRPS I has become popular on the Internet and is often self-diagnosed incorrectly. Websites caution the patient that doctors misdiagnose the condition as hysterical. The result is increasing numbers of hysterical patients seeking consultation for an incorrect, self-diagnosis of CRPS I.
One simple test is to immerse the affected limb in warm water. Wrinkling of the skin of the fingers or toes requires intact sympathetic innervation. The absence of wrinkling is evidence of a lesion in either the central or the peripheral sympathetic pathway. The other, unaffected, limb serves as a control.
Management
Management for most children is range of motion exercise and over-the-counter analgesics. Treatment of more severe syndromes includes the oral administration of guanethidine, gabapentin ( ), prednisone with or without stellate ganglion blockade, and sympathectomy. Pregabalin at doses of 2–10 mg/kg/day divided into two doses often helps.
Erythromelalgia
Familial erythromelalgia is an autosomal dominant disorder (2q24) caused by a mutation in a gene encoding a voltage-gated sodium channel ( ).
Clinical Features
Burning pain occurs in one or more limbs exposed to warm stimuli or exercise. Onset is often in the second decade. Moderate exercise, such as walking, induces burning pain, redness, and warmth of the feet and lower legs.
Diagnosis
The clinical features establish the diagnosis, especially when other family members are affected.
Management
Stopping the exercise provides relief. Sodium channel blockers (carbamazepine, phenytoin, lamotrigine, oxcarbazepine, and possibly lacosamide) are useful to prevent attacks in some families.
Central Congenital Insensitivity (Indifference) to Pain
Most children with congenital insensitivity to pain have an hereditary sensory neuropathy. In many early reports, sensory neuropathy was not a consideration and appropriate tests not performed. This section is restricted to those children and families with a central defect. Sensory neuropathy testing is normal and mild mental retardation often associated. Several affected children are siblings with consanguineous parents. Autosomal recessive inheritance is therefore suspect. The Lesch-Nyhan syndrome is a specific metabolic disorder characterized by self-mutilation (presumably because of indifference to pain) and mental retardation without evidence of sensory neuropathy (see Chapter 5 ).
Clinical Features
Children with congenital insensitivity to pain come to medical attention when they begin to crawl or walk. Their parents recognize that injuries do not cause crying and that the children fail to learn the potential of injury from experience. The result is repeated bruising, fractures, ulcerations of the fingers and toes, and mutilation of the tongue. Sunburn and frostbite are common.
Examination shows absence of the corneal reflex and insensitivity to pain and temperature, but relative preservation of touch and vibration sensations. Tendon reflexes are present, an important differential point from sensory neuropathy.
Diagnosis
The results of electromyography (EMG), nerve conduction studies, and examination of the cerebrospinal fluid are normal.
Management
No treatment is available for the underlying insensitivity, but the repeated injuries require supportive care. Injuries and recurrent infections reduce longevity.
Foramen Magnum Tumors
Extramedullary tumors in and around the foramen magnum are known for false localizing signs and for mimicking other disorders, especially syringomyelia and multiple sclerosis. In children, neurofibroma caused by neurofibromatosis is the only tumor found in this location.
Clinical Features
The most common initial symptom is unilateral or bilateral dysesthesias of the fingers. Suboccipital or neck pain occurs as well. Ignoring such symptoms is common early in the course. Numbness and tingling usually begin in one hand and then migrate to the other. Dysesthesias in the feet are a late occurrence. Gait disturbances, incoordination of the hands, and bladder disturbances generally follow the sensory symptoms and are so alarming that they prompt medical consultation.
Many patients have café au lait spots, but few have evidence of subcutaneous neuromas. The distribution of weakness may be one arm, one side, or both legs; 25 % of patients have weakness in all limbs. Atrophy of the hands is uncommon. Sensory loss may involve only one segment or may have a “cape” distribution. Diminished pain and temperature sensations are usual and other sensory disturbances may be present. Tendon reflexes are brisk in the arms and legs. Patients with neurofibromatosis may have multiple neurofibromas causing segmental abnormalities in several levels of the spinal cord.
Diagnosis
Magnetic resonance imaging (MRI) is the best method for showing abnormalities at the foramen magnum.
Management
Surgical excision of a C2 root neurofibroma relieves symptoms completely.
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