Herpes Zoster Involving the S1 Dermatome
A 19-month-old female infant presented with a 1-week history of ascending linear erythematous eruptions on the left calf. She showed no indications of immune disturbances and was a full-term infant with a healthy rate of weight gain and development. She had been immunized with the varicella vaccine 7 months before presentation. Physical examination revealed a vesicular rash in the S1 dermatome of the left leg (Panel A). A scraping from the base of several vesicles was obtained, and a direct immunofluorescence antigen assay was performed; the results were positive for the varicella–zoster virus. Oral acyclovir was prescribed at a dose of 20 mg per kilogram of body weight per day for 7 days. The lesion improved within a week (Panel B), and there was complete resolution after 2 weeks. Herpes zoster is unusual in persons younger than 10 years of age, and when it does occur in this age group, the lesions have a predilection for dermatomes supplied by the cervical and sacral nerves. In adults, the lesions are more common in the lower thoracic and upper lumbar dermatomes and may involve the trigeminal nerve.
