Viral invasion of the motoneurons and the subsequent inflammation in the anterior horn cells by the varicella zoster virus results in a weakness in the area of the cutaneous eruption. The exact mechanism of zoster paresis is uncertain. The occurrence of symptoms resembling complex regional pain syndrome (CRPS) is common in subjects where the herpes zoster (HZ) outbreak affects an extremity, particularly if it is the distal extremity that is involved. We report the case of a 54-year-old man with monoparesis, hyperalgesia, allodynia, edema, and both color and skin-temperature changes in his left arm after a skin eruption. Electrophysiologic examination revealed the partial degeneration of the superior, middle, and inferior truncus in the brachial plexus, with evidence of HZ infection. Magnetic resonance imaging of the cervical spine and brachial plexus showed degenerative changes without any evidence of nerve root compression. Brachial plexopathy may be the direct cause of the reversible upper-limb paresis resulting from HZ with CRPS-like symptoms.