mononeuritis

Mononeuritis, or mononeuropathy, is the focal impairment of a single peripheral nerve, producing weakness, sensory loss, and sometimes pain in the nerve’s distribution. It is distinguished from polyneuropathy, which involves multiple nerves diffusely, and from mononeuritis multiplex, in which several discrete nerves are affected in an irregular, episodic pattern.

Causes of mononeuritis span several categories. Entrapment or compression neuropathies occur when a nerve is constricted along its course, as in carpal tunnel syndrome (median nerve) or ulnar neuropathy at the elbow. Traumatic injury can damage a specific nerve, leading to abrupt focal deficits. Inflammatory or immune-mediated processes, including vasculitic neuropathies such as those associated with polyarteritis nodosa or granulomatosis with polyangiitis, can selectively affect individual nerves. Infectious causes include herpes zoster, which can inflame a single nerve (radiculopathy or cutaneous neuritis), and leprosy in endemic areas. Metabolic and systemic diseases, tumors, and infiltrative disorders may also produce mononeuropathy by direct involvement or compression.

Clinical presentation typically features focal weakness and sensory loss in the distribution of the implicated nerve, sometimes with neuropathic or aching pain. Diagnosis relies on the history and examination, supported by nerve conduction studies and electromyography, imaging for structural causes, and laboratory tests for inflammatory, infectious, or metabolic etiologies. In some cases, nerve biopsy is necessary to identify vasculitis or infiltrative processes.

Management focuses on treating the underlying cause, relieving compression when possible, and providing symptomatic relief with analgesia and physical therapy. Immunosuppressive therapy may be indicated for inflammatory or vasculitic etiologies. Prognosis varies widely and depends on etiology, severity, and duration before treatment.