Diagnostic approach to peripheral neuropathy

Abstract

Peripheral neuropathy refers to disorders of the peripheral nervous system. They have numerous causes and diverse presentations; hence, a systematic and logical approach is needed for cost-effective diagnosis, especially of treatable neuropathies. A detailed history of symptoms, family and occupational history should be obtained. General and systemic examinations provide valuable clues. Neurological examinations investigating sensory, motor and autonomic signs help to define the topography and nature of neuropathy. Large fiber neuropathy manifests with the loss of joint position and vibration sense and sensory ataxia, whereas small fiber neuropathy manifests with the impairment of pain, temperature and autonomic functions. Electrodiagnostic (EDx) tests include sensory, motor nerve conduction, F response, H reflex and needle electromyography (EMG). EDx helps in documenting the extent of sensory motor deficits, categorizing demyelinating (prolonged terminal latency, slowing of nerve conduction velocity, dispersion and conduction block) and axonal (marginal slowing of nerve conduction and small compound muscle or sensory action potential and dennervation on EMG). Uniform demyelinating features are suggestive of hereditary demyelination, whereas difference between nerves and segments of the same nerve favor acquired demyelination. Finally, neuropathy is classified into mononeuropathy commonly due to entrapment or trauma; mononeuropathy multiplex commonly due to leprosy and vasculitis; and polyneuropathy due to systemic, metabolic or toxic etiology. Laboratory investigations are carried out as indicated and specialized tests such as biochemical, immunological, genetic studies, cerebrospinal fluid (CSF) examination and nerve biopsy are carried out in selected patients. Approximately 20% patients with neuropathy remain undiagnosed but the prognosis is not bad in them.

Keywords: Axonal demyelination; diagnosis; nerve conduction; peripheral neuropathy.

Figure 1

(A) Photograph of a patient with arsenic neuropathy shows Mee's line (B) photograph showing great auricular nerve thickening

Figure 2

Schematic diagram shows topography of deficit inmononeuropathy multiplex, overlap neuropathy and distal symmetrical polyneuropathy

Figure 3

Nerve conduction study of a 52-year-old male with hereditary motor sensory neuropathy showing slowing of conduction velocity and reduced CMAP in (A) ulnar (16.8 m/s; 0.9 mV and 0.8) and median (22 m/s; 0.5 and 0.6 mv) motor conductions. His peroneal and sural conductions were unrecordable. (C) Peroneal conduction study of his son who was asymptomatic showed slowing of conduction velocity (23.6 m/s). (D) Photograph of the patient and his sister and son suggesting AD in heritance. There was wasting and weakness of small muscles of hands and feet of the patient and high-arched feet of the sister and son (inset)