Erythrocytosis (or polycythemia) is the presence of an excessive number of red blood cells in the circulation. It can be primary or arise secondarily to another pathology.
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Terminology
Absolute erythrocytosis is defined as a red cell mass which is >125% predicted for sex and age 2.
Although the diagnosis of erythrocytosis is often put forward when the hemoglobin and/or hematocrit are elevated, they can both be raised, especially the former, yet the red cell mass not be abnormal. Nevertheless if the hematocrit is >0.60 in men or 0.56 in women, then an absolute erythrocytosis is certain 3.
Pathology
Etiology
Following is a list of primary and secondary causes of erythrocytosis.
Secondary etiologies are much more common 1:
Primary
Congenital
erythropoietin receptor (EPOR) mutations
Acquired
genetic (LNK) mutations
Secondary
Congenital
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high oxygen affinity hemoglobins
>100 mutations described
abnormal 2,3 bisphosphoglycerate mutase
-
dysfunctional oxygen-sensing pathway
e.g. VHL mutations
Acquired
Hypoxia-driven
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central hypoxia
chronic lung disease
smoking-related polycythemia
sleep apnea (and other hypoventilation states)
living at high altitude
-
local renal hypoxia
Pathological erythropoietin secretion
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neoplasms
Exogenous erythropoietin
-
drug administration (physician-directed or illicit)
erythropoietin (EPO)
androgens
Radiographic features
Radiographic manifestations are varied and non-specific and can affect a number of systems, including:
-
arterial and venous thromboses
organ infarcts e.g. splenic infarcts
features of extramedullary hematopoiesis
-
increased radiographic attenuation of cerebral arteries, veins and dural sinuses (may mimic cerebral vein thrombosis) on non-contrast CT head 4,5
it is important to consider if increased density may represent a venous sinus thrombosis, in polycythemia the increased density is generally diffuse and not localized to one vessel 4,5
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