corticosteroid ointment (betamethasone valerate) and oral antihistamine, and his eruptions slowly improved. After 2 months of the treatment, his erythema had completely cleared leaving only postinflammatory pigmentation (Fig. 1b).Pityriasis lichenoides is an erythematous, papulosquamous, T cell-mediated dermatosis. 1 Two subtypes are known: the acute type, i.e. classical PLEVA or Mucha-Habermann disease, and a chronic subtype, i.e. pityriasis lichenoides chronica (PLC). The disease duration in PLEVA is not always shorter than that in PLC. 2 The underlying cause of PLEVA is unknown, but various infectious agents have been implicated based on a cluster of cases, familial outbreaks and elevated serum titres to inciting antigens, such as Epstein-Barr virus, T. gondii and human immunodeficiency virus. 3-5 Several reports have demonstrated clonal T-cell receptor rearrangements from PLEVA patient specimens, suggesting that PLEVA is a lymphoproliferative disorder involving T-cell subtypes, despite its clinically benign course and the absence of morphologically atypical cells in the skin lesions. 1,6 Although PLEVA can be found in patients at any age, it occurs predominantly in the second and third decades of life. 5 PLEVA is an uncommon skin disorder in childhood, and infantile cases are extremely rare. As far as we know, only one infantile case of PLEVA has been reported in the English language literature. 2 Gelmitti et al. 2 reported an 8-month-old boy with PLEVA, whose lesions continued for more than 8 years. Our case is one of the first reports of this rare disease in infancy.As a common characteristic in postnatal lymphopoiesis, virtually all T cells in cord blood are derived from the CD45RA (naive) isoform, and a dominance of CD45RA over CD45RO T cells persists during the first 2-3 years of life. Then, the numbers of cells bearing these two isoforms gradually equalize. 7 Cord blood T cells have the capacity to develop an antigenspecific T-cell response from birth, as shown by the vigorous tuberculin reactivity obtained at a few weeks following bacille Calmette-Guérin vaccination even on day 1 of life. These facts indicate that, in general, the T cell-mediated immunity of the infant is immature, but sufficient to be effective.In the present case, CD45RO (LCA)-positive cells were predominant among infiltrating cells in the skin lesion. This result may indicate that T cell-mediated immunity in this patient is comparatively mature. In addition, a large number of CD8+ cells was seen in the skin lesion, similar to the immunohistological features shown in PLEVA in adults. 1 These findings may suggest that, in this infantile case, skin lesions of PLEVA were not a result of an immature immune system or immunological abnormalities such as a skewed distribution of peripheral T cells, but were caused by pathomechanisms similar to those in adult cases.
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