PA29 A case of atypical herpes zoster in an immunocompetent infant with congenital melanocytic naevi

Abstract An immunocompetent 6-month-old child presented with a striking bandlike inflammatory eruption. She was systemically well with no apparent symptoms. Her only medical history was of congenital melanocytic naevi. Brain imaging had not yet been requested. She was exposed to chickenpox at 4 weeks old but had no clinical evidence of primary varicella infection. The patient’s mother had chickenpox in childhood. The patient had crops of grouped vesicles on erythematous bases, on her abdomen and left midback extending onto the left flank. Although perceptibly thoracic dermatomal, the plaques crossed the midline. She also had a large congenital melanocytic naevus overlying the left thoracic region with a number of smaller naevi on her scalp, chest and back. Herpes varicella zoster was confirmed by viral swab. The patient was treated with oral aciclovir and has had complete resolution. Subsequent magnetic resonance imaging confirmed neurocutaneous melanosis. Herpes zoster (HZ) is a segmental eruption due to reactivation of latent varicella zoster virus (VZV) from sensory dorsal ganglia. HZ is typically a painful condition affecting older adults or immunocompromised individuals. Infantile HZ is rare, with an estimated incidence of 0.2 per 1000 person-years in 0–5 year olds (Kurlan JG, Connelly BL, Lucky AW. Herpes zoster in the first year of life following postnatal exposure to varicella-zoster virus: four case reports and a review of infantile herpes zoster. Arch Dermatol 2004; 140: 1268–72). Most cases occur due to intrauterine VZV exposure or early postnatal exposure. Primary infection before 12 months increases the risk of HZ, due to immune system immaturity and less sustained cell mediated immunity. Maternal antibodies can alter primary infection to a subclinical form. Infantile HZ tends to be milder and not associated with complications such as postherpetic neuralgia. Therefore, there is no consensus on whether antiviral treatment is required. Infantile HZ is likely underestimated due to the milder presentation, subclinical primary infections and assumption that maternal antibodies provide protection. Case reports describe vesicles slightly outside the primary dermatome, but to best of our knowledge there are no case reports of eruption crossing the midline. This case highlights the importance of considering HZ as a differential in vesicular eruptions in infants. It highlights the differing presentation where lesions can be asymptomatic and less typically dermatomal. As an additional learning point, this case emphasizes the role of imaging in the presence of large congenital melanocytic naevi to aid diagnosis and prognostication. Early imaging can avoid sedation and increases the sensitivity of detecting melanosis prior to brain myelination in late infancy (Jakchairoongruang K, Khakoo Y, Beckwith M, Barkovich AJ. New insights into neurocutaneous melanosis. Pediatr Radiol 2018; 48: 1786–96).