[1491] Morphology and Immunophenotype of Infectious Mononucleosis Presenting in Axillary and Inguinal Lymph Nodes and Other Unusual Locations

A Louissaint, JA Ferry, NL Harris, LR Zukerberg. Massachusetts General Hospital, Boston, MA

Background: Infectious mononucleosis (IM) due to Epstein-Barr virus (EBV) mainly affects adolescents and young adults, and often results in enlargement of cervical lymph nodes (LN) and Waldeyer ring (WR) tissue.The diagnosis is usually made based on clinical and laboratory findings. Occasionally, IM can present with an enlarged LN or lymphoid mass outside of the cervical and WR region. Such atypical presentations occur most commonly in older patients and a misdiagnosis of lymphoma is not uncommon on biopsy. The morphological and immunophenotypic features of lymphoid tissues in these unusual sites have not been well described.
Design: 10 cases of IM involving inguinal lymph nodes and other unusual sites were identified. Histologic slides were reviewed, immunohistochemistry (IHC) performed, and clinical data obtained from patient records.
Results: Specimens included inguinal LNs (6), axillary LNs (2), conjunctiva (1) and large bowel (1). There were 5 M and 5 F, aged 11 -88 years (median 43). Patients had fever (4/10), splenomegaly (3/10) and/or generalized lymphadenopathy (5/10). Most patients (8/10) had a positive EBV serology. No patient developed lymphoma (f/u 2-96 months [median 36]). LN and mucosal tissues showed architectural distortion by a polymorphous atypical lymphoid infiltrate, often associated with vascular proliferation and a predominance of CD3+ T cells. These features often suggested AITL (4/10). Other cases had bizarre immunoblasts mimicking R-S cells (5/10) that were CD30+, OCT2+ and Bob.1+, but CD15-. The majority of immunoblasts were CD 20+, but in some cases were CD3+CD8+ T cells. Immunoblasts were CD30+(6/6), CD15-(6/6), MUM1+ (3/3), BCL6- (6/6), and CD10- (6/6). BCL2 was variably expressed. Unlike cases of IM in cervical LN/WR, necrosis was not a significant feature (3/10). PCR analysis for T cell rearrangements revealed a small clonal population in 3/10 cases. EBER was positive in all cases.
Conclusions: IM involving extranodal sites other than WR is associated with architectural distortion by an atypical lymphoid infiltrate that may be worrisome for lymphoma on biopsy. IM should be considered in all immunoblastic proliferations - even those occurring in older patients and/or sites outside of the head / neck region. The EBV+ B immunoblasts in IM express MUM1, Oct2, Bob.1, CD30+ and lack CD15, BCL6 and CD10. This expression profile in atypical cells is unusual in DLBCL, T cell lymphoma, and Hodgkins lymphoma, and thus should suggest IM.
Category: Infections

Monday, March 22, 2010 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 203, Monday Morning

 

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