The cause of acute brachial neuritis in the majority of affected patients is undetermined, but more recent research has described several possible etiologic factors to evaluate (4—7). In approximately 25% of the cases, there is a history of having had a recent viral infection, and in 15% of the cases, recent immunizations have been reported. There exist other occasions following surgical intervention where anesthesia for the particular surgery was considered an etiologic factor.

Presentation of individuals with acute brachial neuritis is usually manifest by a sudden onset of severe pain without incident of trauma (8). Sixty-one percent of these occur during the night, and seventy-one percent of the involvement is a single extremity. In 29% of the cases, bilateral upper extremities are involved. The majority of patients have spontaneous weakness of the shoulder girdle musculature, and fortunately, most undergo a spontaneous resolution of the symptoms in a matter of days or weeks. Females resolve their pain both quicker and to a greater degree than males when affected by this problem.

Physical findings predominantly involve the peripheral nerve rather than any type of central manifestation. Profound muscle weakness and fairly substantial atrophy that develops very quickly in the shoulder musculature is observed with this particular entity. There is severe weakness of the deltoid, shoulder rotators, and biceps in the majority of these cases. The upper trunk or the five and six roots seem to be the predominant levels involved. There is usually a decreased tendon reflex, and mild sensory deficits may be present. This is somewhat paradoxical in nature due to the substantial motor loss present on physical examination. Neck symptomatology, such as decreased range of motion or tenderness, is very rare in this disorder.