Radial Mononeuropathy: Clinical and Electrodiagnostic Characteristics in 177 Patients

Radial mononeuropathy is a common peripheral nerve disorder, but comprehensive clinical or electrodiagnostic (EDX) studies remain limited. This study aims to analyze the clinical features, etiologies, and EDX characteristics of radial mononeuropathy.

A retrospective cohort study was conducted on 177 patients (178 lesions) with motor-involved radial mononeuropathy. Lesions were classified by location and etiology into four subgroups: traumatic and nontraumatic, in arm or forearm. Demographics, clinical presentations, and etiologies were compared across subgroups. EDX findings were analyzed, particularly comparing traumatic and nontraumatic arm lesions. Motor nerve fiber involvement was assessed in traumatic and nontraumatic compressive arm lesions.

Most patients had radial mononeuropathy at the arm level, presenting with hyperacute/acute weakness and sensory loss. Common causes included nerve compression (40%) and humeral fractures (18%), while etiologies such as multifocal motor neuropathy and neuralgic amyotrophy were rare. EDX showed motor conduction block (CB) mostly across the spiral groove (67%) but sometimes distally (28%). Preserved sensory responses and demyelinating EDX findings dominated in nontraumatic arm lesions. Extensor indicis proprius (EIP), extensor digitorum communis (EDC), and brachioradialis muscles were most frequently affected. Triceps involvement occurred in 22%-49% of arm lesions. Twenty percent of nontraumatic compressive arm lesions with motor conduction block demonstrated triceps involvement.

Radial mononeuropathy is most commonly caused by nerve compression and humeral fracture. Demyelinating features are strongly associated with nontraumatic lesions. Recording radial motor responses from EIP and EDC improves motor CB detection and localization. Triceps involvement does not always exclude compressive lesions at the spiral groove.