Unilateral Exanthem.

Sir,

A 16-year-old boy presented with a mildly itchy rash on the left side of his body for a week. He had no history of preceding upper respiratory infection or constitutional symptoms. Cutaneous examination revealed a morbilliform rash predominantly over the left side of the abdomen, reaching onto the side of the chest and into the left axilla. The left upper limb was involved as well [Figure 1]. No significantly enlarged lymph nodes were palpable in the draining areas.

Figure 1

Adolescent boy with a unilateral morbilliform eruption involving the left lower chest, abdomen and upper limb. Note the sharp mid-line cut off, and the absence of lesions on the right side

A 35-year-old lady presented with an itchy rash on the left side of her abdomen and over her upper limb for 10 days. There were no constitutional symptoms. She was found to have an eczematous rash over the left side of the abdomen with a sharp midline cut-off, not extending to the chest or axilla, but involving the medial aspect of left forearm as well [Figure 2].

Figure 2

Middle-aged lady with an eczematous eruption on her left abdomen and forearm. Note the sharp mid-line cut off, and the absence of lesions on the right side

Both patients were clinically diagnosed to have unilateral mediothoracic exanthem clinically, treated symptomatically and were reassured of the benign course of the exanthem. The differential diagnosis considered was contact dermatitis, but it was ruled out on the basis of history.

Unilateral mediothoracic exanthem was described as a variant of unilateral laterothoracic exanthem in 2006, where the rash did not extend to the flexures, was characterized by spontaneous remission within a few weeks, with no complications and low infectiousness. Unilateral thoracic exanthema was also suggested as a diagnostic label.[1] Both our patients had abdominal involvement as well. A prospective study of unilateral laterothoracic exanthema revealed that the mean age of patients was 2 years, with a female preponderance of 2:1 and a mean duration of 5 weeks. The morbilliform, eczematous eruption usually began in the axilla.[2] Our patients were both adults, without axillary involvement. The evolution of the rash has been described in two phases, the first being a centrifugal spread for the initial 8 days, followed by a more widespread eruption.[3] The characteristic distribution lead to the change in nomenclature to asymmetric periflexural exanthem of childhood (APEC). The histopathological unique feature is eccrine lymphocytic infiltration.[2] The association of unilateral laterothoracic exanthema with Ebstein Barr virus has been noted in case reports.[45] We propose that the term “Unilateral exanthem” be used for all such exanthems, as they can be laterothoracic, mediothoracic and/or abdominal.