Definition

Neuropathy is a general term indicating nerve disorders of any kind. Myopathy is defined as any disorder with structural changes or functional impairment of muscle.

Pathophysiology

Neuropathies may be caused by certain drugs, diabetes mellitus, human immunodeficiency virus, Lyme disease, leprosy, herpes zoster, Bell palsy, sarcoidosis, and Guillain-Barré syndrome, among others.

Myopathies may be caused by periodic paralyses (hypokalemic, hyperkalemic, and paramyotonia congenita), metabolic alterations of glycolysis (e.g., myophosphorylase deficiency) and fatty acid utilization (e.g., carnitine palmitoyltransferase deficiency), muscular dystrophy, polymyositis, dermatomyositis, fibromyalgia, and polymyalgia rheumatica, among others.

Diagnostic and laboratory findings

Electrodiagnosis is used to diagnose neuropathies. Findings include slowing of nerve conduction velocity, dispersion and reduction in amplitude of evoked action potentials, or conduction block. Nerve biopsy may also be done to determine the cause of the neuropathy.

Muscle biopsy may be used to diagnose specific myopathies. Creatine kinase, which is the preferred muscle enzyme to measure in the evaluation of myopathies, may be elevated. Aspartate aminotransferase, alanine aminotransferase, and lactic dehydrogenase, enzymes in both muscle and the liver, may also be elevated. The erythrocyte sedimentation rate may be elevated in patients with certain myopathies.