Rajkumar, S Vincent

The lack of diagnostic certainty in some patients makes it difficult to distinguish between primary and secondary forms of thrombocytosis. To augment current diagnostic studies for thrombocytosis, we retrospectively evaluated clinical records and bone marrow trephine specimens of 183 patients with thrombocytosis—164 with essential thrombocythemia (ET), 19 with reactive thrombocytosis (RT)—for bone marrow angiogenesis, bone marrow megakaryocyte c-Mpl staining, and morphologic evidence of megakaryocyte proliferation. Angiogenesis was increased in patients with ET compared with healthy controls (P < .0001) and patients with RT (P = .006). In addition, an increase in angiogenesis was associated with certain disease features such as splenomegaly (P = .004) and reticulin fibrosis (P = .005). Decreased megakaryocyte c-Mpl staining was observed in a heterogeneous pattern in ET compared with healthy controls (P < .0001) and RT (P < .0001). Histologic stratifying criteria incorporating increased angiogenesis, decreased megakaryocyte c-Mpl expression, and marked megakaryocyte proliferation in the bone marrow was highly sensitive (97%) and specific (95%) for distinguishing ET from RT (P < .0001). However, with the current duration of follow-up available on the patients, none of the histologic features evaluated have yet demonstrated prognostic value for subsequent clinical course, vascular events, or survival.

Primary systemic amyloidosis (AL) is a plasma cell (PC) dyscrasia with clinical similarities to multiple myeloma (MM) and monoclonal gammopathy of undetermined significance (MGUS), but its molecular basis is poorly understood. Translocations at the immunoglobulin heavy-chain (IgH) locus, 14q32, are likely early genetic events in both MM and MGUS and involve several nonrandom, recurrent, partner chromosomes such as 11q13, 16q23, and 4p16.3. Given the similarities between MM, MGUS, and AL, bone marrow clonal PCs were evaluated in 29 patients with AL using interphase fluorescence in situ hybridization (FISH) combined with immunofluorescence detection of the cytoplasmic light-chain (cIg-FISH) for the presence of 14q32 translocations and the t(11;14)(q13;q32). Of 29 patients studied, 21 (72.4%) showed results compatible with the presence of a 14q32 translocation, and 16 (76.2%) of those had translocation (11;14)(q13;q32) for an overall prevalence of the abnormality of 55%. IgH translocations are common in AL, especially the t(11;14)(q13;q32).