Erythrodermic Mycosis Fungoidosis with CD1a+ Dendritic Cell Hyperplasia, a Mimic of Langerhans Cell Histiocytosis

Mycosis fungoides is the most common primary cutaneous T cell tumor. We present a caseof MF with misdiagnosis of langerhans cell histiocytosis indicating prominent LCproliferation that cause a difficult distinction between reactive LC proliferation and LCH.The different skin features of mycosis fungoides morphologically mimicking other entitiessuch as LCH,therefore the correct diagnosis is based on considering the both clinical andhistopathological findings of MF.Introduction:Although CD1a(+) dendritic cells (DC) in cutaneous T-cell lymphoma have been welldocumented, the presence of large numbers of DC within lymphoid infiltrates can pose adiagnostic difficulty.Case Report:We present a case of 69-year-old man with a 2-year history of recurrent red nodules on theextremities that was referred to pathology laboratory with the previous diagnosis oflangerhans cell histiocytosis. The slides from skin nodule (2 years ago) were reviewed thatshowed severe cellular infiltration in the superficial and deep dermis consisting of epitheloidcells with grooved nuclei and eosinophilic cytoplasm, which reacted with antibodies of CD1aand S-100 in staining but negative results with CD68. Otherwise, less prominent populationof atypical small lymphocytes admixed with eosinophils observed. The previous pathologicreport was consistent with Adult- type cutaneous langerhans cell histiocytosis. Now, thepatient s biopsy specimen referred to us with clinical diagnosis of sezary syndrome.Histopathologically, the lesion showed a band like infiltrates of small to medium-sized,irregular and angulated atypical lymphoid cells admixed with less population of LC and rareeosinophils. We also observed epidermotropism of atypical lymphoid cells. In peripheralblood film no sezary cells were identified and in flow cytometric analysis the ratio ofCD4:CD8 was 0.5 .White blood cells and platelet count were normal. Liver function testswere within normal limits. Serum anti HTLV-1/2 measurement was negative. Clinicalmanifestations, histopathological and flow cytometric features suggest diagnosis oferythrodermic stage of mycosis fungoides.Discussion:Cutaneous DCs play an important role in the induction of immune response against tumorcells. In the other study, same as our case, the proportion of LCs intermingled with malignantlymphoid cells in the tumor stage infiltrate is significantly higher than that in the patch/plaque stage infiltrates. The presence of pronounced infiltrates of CD1a+/S-100 + LCsamong atypical lymphoid cells in the tumor stage MF lesions may lead to misinterpretation asLCs histiocytosis (LCH) histopathologically .Although LCH is a different disease entitycaused by the infiltration of LCs in one or more organs, among which cutaneous involvementis considered to portend a multisystemic involvement and has a poor prognosis .Previousstudies demonstrated that LCH is characterized by clonal proliferation. The LCs of LCH forma monoclonal population, indicating that LCH is neoplastic. However, other studies state thatthe excess of LC in lymphoproliferative disorders or lymphoma is polyclonal. This maysupport that the accumulation of LC in this circumstance is in favor of a reactive nature.Conclusion:This case indicates that prominent LC proliferation may cause a difficult distinction betweenreactive LC proliferation and LCH.

کلیدواژه ها:

Mycosis fungoides ، Reactive CD1a+ Dendritic cell hyperplasia ، Langerhans cell histiocytosis