Conduction block of varicella zoster virus neuropathy

Case report.

A 64-year-old woman noticed swelling of her right index finger followed by dysesthesia, reddening of the skin, and vesicle in the area from the right shoulder to the palm. She was diagnosed with herpes zoster and treated with acyclovir IV. She had been treated for chronic myelocytic leukemia (CML, chronic stage) since 1992. Four weeks later she noticed weakness of her right upper extremity that progressed slowly. She was admitted to our hospital 2 months later. Physical examination revealed pigmentation of skin in the right C6 and C7 dermatomes. Cranial nerves were intact. Manual muscle testing revealed weakness in the right upper extremity, which did not correspond to individual myotomes: deltoid (4/5), biceps (4/5), brachioradialis (4/5), triceps (3/5), extensor carpi radialis (3/5), extensor digitorum (3/5), abductor pollicis brevis (2/5), flexor digitorum superficialis (1/5), abductor digiti minimi (4/5), and dorsal interossei (4/5) (MRC rating scale). There was mild hypesthesia and hyperalgesia in the median-innervated area of the right palm. Deep tendon reflexes were absent in the right upper extremity. White blood count was 3,900/μL. C-reactive protein was slightly elevated (4.9 mg/dL). Sedimentation rate was 75 mm/hour. Antinuclear antibody and p-ANCA were negative. The serum titer of anti-VZV immunoglobulin (Ig) M was negative, but that of anti-VZV IgG was elevated. Cell numbers, protein level, sugar, and IgG index in the CSF were normal. Nerve conduction study revealed conduction block and conduction velocity slowing of the right median nerve in the forearm (figure, A). Conduction block was also demonstrated between the cubitus and brachial plexus of the right radial nerve (figure, B). Needle EMG showed active neurogenic change in the right triceps muscles suggesting the involvement of the part between spiral groove of the upper arm and brachial plexus. MRI of the right forearm demonstrated extensive lesions in the connective tissue around the finger flexor tendons and muscles along the median nerve. There was no compressive mass in the forearm such as chloroma (local collection of blast cells), which may be seen in CML. Oral administration of prednisolone improved the strength of abductor pollicis brevis (3/5), the conduction blocks of the two nerves, and the lesions on MRI.

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Figure. (A) Right median compound muscle action potentials (CMAP) recorded from the thenar muscle of the patient. The sites of stimulation include 2.5, 3.7, and 5.7 cm proximal to the distal crease at the wrist and elbow. The median sensory response was absent. This study demonstrated focal conduction block and slowing in the lower forearm segment. One month later, the CMAP with stimulation 3.7 cm proximal to the wrist increased from 0.31 to 1.24 mV. (B) Right radial CMAP recorded from the extensor carpi ulnaris muscle. The sites of stimulation include the mid forearm, above the elbow, proximal to the spiral groove, and Erb point. The median and ulnar nerves were stimulated above the elbow simultaneously as a reference. Conduction block was observed between cubitus and brachial plexus.

Discussion.

Our case was an immunocompromised host owing to CML, and the reactivation of VZV seemed to occur in the dorsal root ganglia, resulting in sensory disturbances and skin lesions first. After the appearance of usual symptoms of herpes zoster, motor involvement occurred at the level of peripheral nerves. Electrophysiologic study demonstrated the conduction block at uncommon sites of two different nerves. These findings suggested that the Schwann cells of the motor nerves were damaged locally by viral direct invasion or allergic mechanisms. In addition, we observed abnormal signals in the connective tissues along the median nerve on MRI. As the lesions were diminished by steroid therapy, they probably reflected the inflammatory changes.

Motor involvement of herpes zoster has been reported usually as segmental zoster paresis, and rarely polyneuritis (Guillain-Barré syndrome), but there is no report of conduction block of peripheral nerves associated with VZV infection presenting with mononeuritis multiplex. In segmental zoster the responsible lesions for motor involvement are considered to be anterior horn or anterior root, to where the inflammation in the ganglia extends.2,3⇓ In respect to polyneuritis after zoster, the segmental demyelination and remyelination of the nerves was described in two patients.4 There are only a few reports of mononeuropathy,2,5⇓ in which motor nerve demyelination was suggested in four cases by electrophysiologic findings (disproportionate conduction slowing or temporally dispersed compound muscle action potentials).

Abnormal MRI findings have been reported in the cauda equina, spinal nerves, cord, cranial nerves, pons, cerebral white matter, and meninges in VZV infection.1,6⇓ We applied MRI to examine the conduction block of our patient. Abnormally increased short-tau inversion recovery signals were observed stronger in the flexor tendon and muscle interspaces along the median nerve than the muscle itself. Although acute denervation of muscle might change the MRI signal in some part, the extensive lesions in the right forearm mainly reflected the extension of VZV infection to connective tissues along the median nerve. As the patient was immunosuppressed, VZV might be disseminated to the Schwann cells and fibroblasts.1,7⇓