C5-Predominant Segmental Zoster Paresis Presenting With Right Shoulder Abduction Weakness Before Cutaneous Eruption: A Case Report.

Segmental zoster paresis (SZP) is an uncommon motor complication of herpes zoster (HZ) characterized by focal, asymmetric weakness in a myotomal distribution. Motor weakness usually follows the cutaneous eruption, and pre-eruptive weakness can mimic cervical radiculopathy, brachial plexopathy, neuralgic amyotrophy, or other causes of acute focal limb weakness. A 57-year-old woman developed right shoulder pain and, five days later, became unable to abduct her right arm. A vesicular eruption appeared on the lateral aspect of the right upper arm three days after the onset of weakness, and HZ was diagnosed. Examination showed C5 dermatomal vesicular lesions, severe pain, and right deltoid weakness of 2/5 on manual muscle testing. T2-weighted magnetic resonance imaging revealed hyperintensity and enlargement of the right C4 and C5 nerve roots. Nerve conduction studies of the median, radial, and ulnar nerves were normal; needle electromyography and axillary nerve conduction studies were not performed. The clinical and imaging findings supported a diagnosis of C5-predominant SZP, with localization most consistent with zoster-associated cervical radiculopathy. She received intravenous acyclovir and two courses of methylprednisolone pulse therapy. By hospital day 11, right deltoid strength had recovered to 5/5, and pain had decreased to 1/10. This case highlights the importance of considering pre-eruptive zoster-associated motor involvement in patients with acute painful focal limb weakness. Serial skin examinations and careful neurologic localization may facilitate timely diagnosis.