Unclassifiable non-CML classical myeloproliferative diseases with microcytosis: findings indicating diagnosis of polycythemia vera masked by iron deficiency
Background/aim
Polycythemia   Vera   (PV)   is   a   myeloproliferative   disorder   characterized   by   overproduction   of   morphologically  normal  red  blood  cells  (RBCs),  granulocytes,  and  platelets,  a  phenotype  that  is  caused  by  a  mutation  (V617F)  in  Janus  kinase  2  (JAK2).  However,  JAK2 V617F  is  also  found  in  approximately  50%  of  patients  with  essential  thrombocytosis and primary myelofibrosis, rendering its presence nonspecific as a diagnostic test. An increased red cell mass  is  a  major  criterion  for  the  diagnosis  of  PV  according  to  World  Health  Organization  (WHO)  2016  criteria.  High  hemoglobin (Hgb) or Hematocrit (Hct) are universally used as indicators of an increased red cell mass for the diagnosis of PV. However, conditions such as iron deficiency (ID) with decreased mean cell volume may mask the diagnosis due to nonelevated Hct level. The aim of this study was to investigate the clinical characteristics of the patients with unclassifiable non-CML classical myeloproliferative disease with microcytosis (MPD/M) and nonelevated Hgb and Hct levels at diagnosis and to determine if some of these cases could be real PV cases masked due to ID-related microcytosis.


Materials and methods
There were 23 MPD/M cases among 208 non-CML classical MPD cases (11%). Among 22 patients who had adequate test results related to the cause of microcytosis, ID and beta-thalassemia trait (TT) were the apparent causes of microcytosis in 15 and 1 cases, respectively.


Results
Clinicopathological  correlations  revealed  consistently  positive  JAK2  V617F  mutation  status  (20/20,  100%),  frequently elevated RBC count (17/23, 73.9%), and PV-compatible bone marrow findings (10/12, 83.3%). These findings are compatible with PV instead of essential thrombocytopenia or primary myelofibrosis. In spite of frequent cytoreductive treatment, 3 patients developed increased Hgb/Htc levels during median 58.2 (279–63) months’ follow-up.


Conclusion
These data show that the majority of MPD/M cases are PV patients masked due to ID-related microcytosis.