Neurology

ICD-9 Code: 356.9.

Classification: Several patterns of peripheral neuropathy are relevant to rheumatologic disorders: (a) mononeuropathy involvement of one nerve, (b) mononeuritis multiplex-sequential peripheral nerves are affected usually in an asymmetric fashion, and (c) polyneuropathy-symmetric involvement of multi-ple sensory and/or motor nerves.

Etiology: Rheumatologic diseases most commonly associated with peripheral neuropathy include the vasculitides (particularly PAN), cryoglobulinemia, RA, SLE, Sjögren’s syndrome, and amyloidosis. Vasculitis leading to mononeuritis multiplex, for example, commonly results in a mixed sensorimotor axonal neuropathy. Lyme disease may lead to a facial nerve (Bell’s) palsy and, less commonly, a sensory radiculoneuritis. Peripheral neuropathy may also result from compression, trauma, or injury of a nerve root as it emerges from the spinal cord (radiculopathy), in the brachial plexus (plexopathy), or more distally (focal nerve entrapment) (Table 26). Entrapment neuropathies are often caused by noninflammatory mechanical trauma but may also be owing to abnormal nerve compression, such as median nerve mononeuropathy (CTS) in a patient with wrist synovitis (e.g., RA) or progressive degenerative conditions (e.g., diabetes mellitus).

Pathology: Mononeuritis multiplex results from vasculitis and vascular ischemia of the vessels supplying the nerve (vasa nervorum). In amyloidosis, polyneuropathy is believed to be caused by amyloid deposition in or around nerves that alter nerve conduction. Sensory polyneuropathy sometimes seen in Sjögren’s syndrome may be caused by small vessel vasculitis and dorsal root ganglionitis. Entrapment neuropathy results from nerve compression, leading first to sensory and then motor deficits.

Cardinal Findings: Painful burning dysesthesia and motor weakness are the hallmark symptoms of peripheral neuropathy. Muscle atrophy, paresthesia, and frank sensory deficits may follow. Foot drop (lower extremity symptoms occur more commonly than upper extremity ones) or wrist drop in a patient who is systemically ill with multiple organ disorder may indicate mononeuritis multiplex owing to PAN or another form of systemic vasculitis.

Diagnostic Testing: Electrodiagnostic evaluation by EMG (see p. 69) and sensory/motor nerve conduction studies (see p. 90) helps to pinpoint the areas affected and may elucidate the specific type of abnormality. In peripheral neuropathy, EMG usually show fibrillation potentials and positive sharp wave owing to muscle denervation. Nerve conduction studies show reduced amplitudes with relatively normal sensory and motor conduction velocity. In mononeuritis multiplex, biopsy of the sural nerve is often performed to look for evidence of vasculitis in the vasa nervorum. The nerve itself may show axonal degeneration and, occasionally, patchy demyelination. Other laboratory studies potentially helpful in confirming the cause of an underlying inflammatory disorder should be dictated by the history and physical examination. Useful studies may include CBC, serum creatinine, urinalysis, chest x-ray, ANA, RF, cryoglobulins, hepatitis serology, immunoelectrophoresis, and ANCA.

Keys to Diagnosis: A comprehensive neurologic examination with particular attention to the sensory components of the examination is essential. Diminished vibratory and position sense are sensitive indicators of early peripheral neuropathy.

Therapy: If the neuropathy is caused by an active inflammatory process (e.g., a vasculitis), then systemic corticosteroids alone or in combination with immunosuppressive agents are frequently indicated, with the dosage dictated by the specific disorder and its severity. Compressive lesions such as CTS may respond well to local measures (e.g., splinting) or surgical release. Physical modalities and rehabilitative services, including appropriate use of splints, braces, and occupational and physical therapy, are frequently very appropriate. Infrequently, agents such as tricyclic antidepressants or carbamazepine are used to alleviate neuropathic pain.

Prognosis: The course and prognosis are highly influenced by the underlying pathologic mechanisms and systemic response to antiinflammatory therapy, if indicated.

BIBLIOGRAPHY
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