Mycoplasma pneumoniae-associated Stevens-Johnson syndrome exhibits lymphopenia and redistribution of CD4⁺ T cells

Erythema multiforme (EM) an immune-mediated disease categorized into EM minor and EM major, also called Stevens-Johnson syndrome. The presence of mucosal involvement differentiates erythema multiforme major from erythema multiforme minor. Many drugs and agents can induce Stevens-Johnson syndrome. We report a case of Stevens-Johnson syndrome associated with Mycoplasma pneumoniae infection. Lymphopenia with a significant decrease of CD4⁺ T cell in the blood and predominant CD4⁺ T cells in the skin vesicular fluid was found. The improvement of lymphopenia was associated with disease recovery. In a retrospective chart review of patients treated in our hospital over the past 3 years, we found that 5 patients with Stevens-Johnson syndrome all had lymphopenia (< 1.5 × 10⁹/L; average 0.99 × 10⁹/L), whereas 13 other patients with erthema multiforme minor demonstrated normal lymphocyte counts (average 3.13 × 10⁹/L), with the exception of one patients with herpes infection showing lymphopenia. There results suggested that an immunopathologenesis involving redistribution of CD4⁺ T cells might contribute to the development of Stevens-Johnson syndrome. Further studies to investigate the involvement of CD4⁺ T cells in Stevens-Johnson syndrome may implicate a specific strategy to prevent fatal Steven-Johnson syndrome.