Despite the fact that some of the vesicles crossed the midline (which is suggestive of disseminated zoster), the FP felt confident in diagnosing herpes zoster (shingles) in this patient. The FP knew that the varicella-zoster virus (VZV) leaves the dorsal root ganglion to travel down the spinal nerves to the cutaneous nerves of the skin. But she also knew that the vesicles could cross the midline by a few centimeters because the posterior primary ramus of the spinal nerve includes a small cutaneous medial branch that reaches across the midline.1
After a primary infection with either chickenpox or vaccine-type VZV, a latent infection is established in the sensory dorsal root ganglia. Reactivation of this latent VZV infection results in herpes zoster. Both sensory ganglia neurons and satellite cells surrounding the neurons serve as sites of VZV latent infection. Once reactivated, the virus spreads to other cells within the ganglion. The dermatomal distribution of the rash corresponds to the sensory fields of the infected neurons within the specific ganglion.
The pain associated with zoster infections and postherpetic neuralgia (PHN) is thought to result from injury to the peripheral nerves and altered central nervous system processing. PHN occurs more commonly in individuals older than age 60 and in immunosuppressed individuals. The lesions typically crust in approximately a week, with complete resolution within 3 to 4 weeks. If there are more than 20 lesions distributed outside the affected dermatome, the patient has disseminated zoster.
The treatment of herpes zoster includes antiviral agents, such as acyclovir, famciclovir, and valacyclovir. The evidence only supports their use if started within 72 hours of rash onset. Pain can be managed with nonprescription analgesics or narcotics and should be treated aggressively. This may actually prevent or lessen the severity of PHN.
The FP in this case was also concerned about whether the patient might be positive for human immunodeficiency virus (HIV) or have some type of immunosuppression. The patient denied sexual activity and use of intravenous drugs (even when her mom wasn’t in the room). She was otherwise healthy, so no further workup for HIV or immunosuppression was ordered. The FP told the teen to stay home from school until the lesions crusted over. A follow-up visit in one month was scheduled. The zoster resolved and the girl returned to her usual state of good health.
1. Usatine RP, Clemente C. Is herpes zoster unilateral? West J Med. 1999;170:263.
Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Mayeaux EJ, Usatine R. Zoster. In: Usatine R, Smith M, Mayeaux EJ, et al, eds. Color Atlas of Family Medicine. 2nd ed. New York, NY: McGraw-Hill; 2013:712-717.
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