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Persistent rash on the sole

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Differential includes vesiculobullous conditions

There are several important items to consider in the differential.

Cutaneous vasculitis, in severe cases, may manifest with vesicles or bullae that resemble the lesions seen in HZ. However, its unilateral nature and distribution distinguish it.

Angioinvasive fungal infections in immunocompromised patients may manifest with scattered ulceronecrotic lesions to purpuric vesiculobullous dermatoses.9 However, no fungal organisms were seen on GMS staining of the biopsied tissue.

Atypical hand-foot-and-mouth disease tends to affect adults and is associated with Coxsackievirus A6 infection.10 It may manifest as generalized vesiculobullous exanthem resembling varicella. The chronic nature and restricted extent of the patient’s rash made this diagnosis unlikely.

Successful management depends on timely identification

Although most cases of HZ can be diagnosed clinically, atypical rashes may require a biopsy and direct immunofluorescence assay for VZV antigen or a polymerase-chain-reaction (PCR) assay for VZV DNA in cells from the base of blisters. Therefore, it is important to consider the diagnosis of HZ in immunocompromised patients presenting with an atypical rash to avoid misdiagnosis and costly testing.

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