Absent neutrophil alkaline phosphatase in the eosinophilia myalgia syndrome associated with L-tryptophan use

The clinical constellation of leukocytosis, thrombocytosis, and low or absent stainable neutrophil alkaline phosphatase (NAP) is considered characteristic of chronic myelogenous leukemia (CML). CML with eosinophilic differentiation (eosinophilic leukemia) is well described, and leukemia and other clonal hematologic malignancies are associated with the syndrome of eosinophilic fasciitis. We describe leukocytosis, thrombocytosis, eosinophilia, mild basophilia, and absent stainable NAP, initially suggesting the diagnosis of CML in a patient with the eosinophilia myalgia syndrome associated with L-tryptophan use, a condition resembling eosinophilic fasciitis. Cytogenetic and molecular genetic studies failed to demonstrate a clonal proliferation of eosinophils.