TEMPI syndrome (telangiectasias, elevated erythropoietin level and 
erythrocytosis, monoclonal gammopathy, perinephric fluid collections, and 
intrapulmonary shunting) is a recently described syndrome that, owing to 
erythrocytosis, may be confused with polycythemia vera. It is best classified as 
a type of plasma cell dyscrasia with paraneoplastic manifestations, similar to 
POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, M-protein, and 
skin abnormalities). To date, 11 patients have been identified. This is the 
first morphologic review of TEMPI syndrome bone marrow samples, in order to 
define pathologic features that may aid in the recognition of the syndrome and 
to identify post-therapy changes. Seven bone marrow aspirates and biopsies from 
three patients, including two post-treatment marrows, were examined. Patients 
were 36, 49, and 49 years old at time of diagnosis. In all cases, erythropoietin 
levels were extremely elevated at >5000 IU/l, the paraprotein was IgG kappa, 
JAK2 V617F was negative and vascular endothelial growth factor levels were 
normal. In one case, the increase in clonal plasma cells reached levels of 
smoldering myeloma (18%), but remaining marrows showed few monoclonal plasma 
cells (<5%). All pre-treatment biopsies showed erythroid hyperplasia, with mild 
nonspecific megakaryocytic, and erythroid cytologic atypia in one marrow. 
Prominent plasma cell vacuolization and reactive-appearing lymphoid aggregates 
were noted in one case. Findings of myeloproliferative neoplasms, including 
megakaryocyte clusters and fibrosis, were not identified. In conclusion, TEMPI 
syndrome should be considered when erythrocytosis and plasma cell dyscrasia 
coexist. The bone marrow findings, although nonspecific, differ significantly 
from polycythemia vera. Peculiar clinical and laboratorial findings of TEMPI, 
including elevated erythropoietin and normal vascular endothelial growth factor 
level, allow the diagnosis and distinction from POEMS syndrome. Significant 
decrease in erythropoietin level following treatment suggests a role of 
erythropoietin in monitoring therapeutic response.