mononeuropathies

Mononeuropathies are focal peripheral nerve disorders that affect a single nerve or a single nerve root distribution, leading to symptoms such as weakness, numbness, and pain in the area supplied by that nerve. They are distinguished from polyneuropathies, which involve many nerves in a symmetric fashion, and from mononeuritis multiplex, which affects several noncontiguous nerves.

Common causes include trauma and compression, such as carpal tunnel syndrome (median nerve at the wrist), ulnar neuropathy at the elbow, radial neuropathy at the proximal arm, and common peroneal neuropathy at the fibular neck. Ischemic injury, inflammatory processes (including vasculitis), infections, and iatrogenic injury from surgery or injections can also produce mononeuropathies. Less commonly, nerve inflammation or infectious processes such as herpes zoster may present as a focal neuropathy.

Diagnosis relies on clinical localization of deficits to a specific nerve distribution, supported by diagnostic testing. Nerve conduction studies and electromyography help determine whether the lesion is axonal or demyelinating and identify the affected nerve. Imaging, including MRI or ultrasound, can reveal nerve compression, swelling, or proximal pathology. Laboratory evaluation may be guided by clues to systemic disease (e.g., diabetes, vasculitis, autoimmune conditions) to identify treatable etiologies.

Management aims to alleviate symptoms and address the underlying cause. Treatment may include splinting or physical therapy to preserve function, surgical decompression or nerve release when compression is documented, and avoidance of further injury. Pain management may involve analgesics and neuropathic pain medications. Prognosis varies with the cause, duration of symptoms before treatment, and whether nerve regeneration can occur; focal compressive lesions often improve after decompression, while severe axonal injury may recover more slowly or incompletely.