Abstract

Mycosis fungoides (MF) is the most common form of cutaneous T-cell lymphoma. Rare biologically distinct variants include folliculotropic MF, pagetoid reticulosis, and granulomatous slack skin. Interstitial MF represents an uncommon histologic variant that may mimic an inflammatory dermatosis. In the largest published series of IMF, most patients present with patches and plaques of conventional MF during the disease course and have stage I disease. Here, we present an 85-year-old Caucasian man who presented with right-sided abdominal pain and edema for 8 months described clinically as “lymphedema”. Computed tomography scan showed mildly prominent inguinal nodes on the right. Punch biopsy of the right abdomen showed a fibrotic dermis and an interstitial infiltrate of small lymphocytes displaying nuclear hyperchromasia and irregular nuclear contours. An epidermotropic infiltrate of similar-appearing lymphocytes was found along the dermoepidermal junction. Immunohistochemistry was performed and demonstrated that lymphocytes express CD3, CD8, CD2, TCRβF1, and TIA1 and lack expression of CD7, TCRΔ, granzyme B, and CD56. CD68 and CD4 highlighted predominantly interstitial histiocytes. T-cell clonality studies demonstrated a clonal T-cell population. In conjunction with the clinical findings, a diagnosis of interstitial mycosis fungoides (IMF) was made. Given the unusual clinical findings without typical patches and plaques of conventional MF, knowledge of IMF is critical to prevent misdiagnosis of an inflammatory dermatosis.