Abstract

A 69-year-old male presented to dermatology clinic with a 2-year history of a progressive, pruritic erythematous rash involving the right chest and arm which began shortly after a right shoulder injury and subsequent replacement surgery. Notably, the patient had no history of radiation, immunosuppression or rheumatoid arthritis. Apixaban and clopidogrel started for atrial fibrillation during course of the rash had no effect on it. Examination demonstrated indurated erythematous reticulated plaques of the right chest and arm. Punch biopsies of the eruption were performed revealing ectatic vascular spaces filled with mononuclear cells in the deep dermis. The intravascular mononuclear cells were composed of a mixture of CD3 and CD20 positive lymphocytes and CD68 positive histiocytes. The T-lymphocytes showed a balanced expression of CD4 and CD8 with no significant loss of CD7. There was no light chain restriction on kappa and lambda in-situ hybridization. CD31 and D2-40 stains highlighted ectatic vascular spaces. HHV-8 and c-MYC stains were negative. Additional PU.1 staining was performed during outside consultation which was positive in many of the intravascular mononuclear cells, confirming histiocyte origin. Given the histopathologic and immunohistochemical features, a diagnosis of intravascular histiocytosis was made.  Intravascular histiocytosis is a rare skin condition, favored to be a reactive inflammatory process and often occurs in association with prosthetic joints, trauma, surgery or rheumatoid arthritis. Due to the under recognition and varied clinical appearance, biopsy with appropriate immunohistochemical staining is necessary to rule out more ominous entities such as angiosarcoma and intravascular lymphoma and carcinomas.