An 86-year-old woman presented to her General Practitioner with a 3-week history of sweats and a vasculitic rash on her lower limbs. A blood count and film showed isolated mild thrombocytopenia (platelet count 81 × 109/l) and a few myelocytes but was otherwise unremarkable. Two weeks later she was admitted to hospital with acute severe dyspnoea, eventually ascribed to chronic obstructive pulmonary disease, and a macular, erythematous facial rash. Investigations showed an erythrocyte sedimentation rate (ESR) of 99 mm in 1 h, polyclonal hypergammaglobulinaemia, and a lactate dehydrogenase of 945 U/l. The haemoglobin was 11·6 g/dl, leucocyte count 13·9 × 109/l with an eosinophil count of 1 × 109/l, and platelet count of 36 × 109/l. The blood film was leucoerythroblastic with a pleomorphic population of atypical lymphoid cells (7·4 × 109/l). These were small with lobulated or indented nuclei, mature chromatin, with some having perinuclear pallor (left). In many of these cells the cytoplasm contained multiple very small vacuoles, giving a ‘frothy’ appearance (left, top left quadrant). A small number had eccentric nuclei and some of these contained coarse, deeply azurophilic granules (left, top quadrants). Flow cytometry of the lymphoid cells showed that they expressed CD2, CD4, CD5 and CD10 (right). The majority were negative for CD3, CD7, CD16 and CD56. T-cell clonality was demonstrated by detection of clonal rearrangements of TCRG and TCRD genes.
Monoclonal proliferation of CD10-positive mature T cells is a hallmark of angioimmunoblastic T-cell lymphoma. The clinical and other laboratory features of this case, including lack or reduced expression of CD3, are also typical of this diagnosis. Angioimmunoblastic T-cell lymphoma is normally diagnosed on tissue biopsy, usually lymph node biopsy. In this case, the diagnosis was made on the morphological and phenotypic features and clonality of abnormal circulating lymphoid cells. The patient died of a myocardial infarction a few days after admission and so no further investigation or tissue biopsy was possible. Morphology and immunophenotyping of the peripheral blood may provide rapid diagnosis of this aggressive disease as leukaemic spread does occur.