A definitive diagnosis of mucosa-associated lymphoid tissue lymphoma made at a second biopsy.

INTRODUCTION: A case of mucosa-associated lymphoid tissue (MALT) lymphoma, the most frequent of the various conjunctival lymphoproliferative disorders, in which the initial biopsy was inconclusive but the second biopsy provided a definitive diagnosis, is reported.

CASE REPORT: A 26-year-old woman with a 3-month history of bilateral conjunctival swelling was referred by a local physician for suspected MALT lymphoma. A salmon-pink elastic swelling was found to involve both eyes and to extend from the lower palpebral conjunctiva to the bulbar conjunctiva. Tonsillar swelling was also found, and ophthalmologic (left eye) and otolaryngologic biopsies were therefore performed simultaneously under general anesthesia. The otolaryngologic diagnosis was chronic tonsillitis. Light microscope examination of the conjunctival tissue showed proliferation of lymphocytes and small aggregates of small to medium-sized atypical lymphocytes. On immunohistochemical studies, atypical lymphocytes were positive for CD20 and CD79a, but differentiation to plasmacytes was not prominent, and neither Dutcher bodies nor evidence of immunoglobulin light chain restriction was found. The results were not incompatible with MALT lymphoma but were not definitive. A second biopsy of the right eye was therefore performed 3 months later. Staining with hematoxylin and eosin showed proliferation of small lymphocytes and monocytoid B cells and differentiation to plasmacytes. The hyperplastic cells were positive for CD19, CD79a, and CD20, and their cytoplasm were positive for Bcl-2 and slightly positive for Bcl-6. Cells positive for CD38 were noted where differentiation to plasmacytes and immunoglobulin light chain κ restriction was evident on immunohistochemical studies and in situ hybridization. The Ki-67-positivity rate was approximately 5%. The results of paraffin-embedded tissue section fluorescence in situ hybridization were negative for MALT-1 (18q21). A diagnosis of MALT lymphoma was made, and treatment with rituximab was started.

DISCUSSION: Few findings lead directly to a definitive diagnosis of MALT lymphoma, and its differential diagnosis from benign lymphoproliferative disorders is difficult. In the present case definitive diagnosis was possible only after a second biopsy. This case suggests repeated biopsy may be necessary when a single biopsy is not definitive.