Secondary polycythemia (ORPHA:98428)
Secondary polycythemia is an elevated absolute red blood cell mass caused by enhanced stimulation of red blood cell production by an otherwise normal erythroid lineage that may be congenital or acquired (congenital secondary polycythemia and acquired secondary polycythemia; see these terms).
Epidemiology
Prevalence is unknown.
Clinical description
Clinical features vary according to the origin of the disease but may include plethora or ruddy complexion, headache and tinnitus. The congenital form may be complicated by superficial or deep vein thrombophlebitis, or present with associated symptoms as in Chuvash erythrocytosis (see this term), or the course of the disease may be indolent. Patients with a specific sub-type of congenital secondary polycythemia, known as Chuvash erythrocytosis, present with lower systolic or diastolic blood pressure, venous varicosities, and vertebral body hemangiomas and may be complicated by cerebrovascular events or mesenteric thrombosis. The acquired form of secondary polycythemia may present with cyanosis, hypertension, clubbing of the fingers and toes and lethargy.
Etiology
Secondary polycythemia may be congenital and caused by defects in the oxygen sensing pathway due to autosomal recessive mutations in the VHL, EGLN1 and EPAS1 genes (3p26-p25, 1q42-q43 and 2p21-p16 respectively) which result in enhanced erythropoietin (EPO) production in hypoxic conditions, or by other autosomal dominant congenital defects including high oxygen-affinity hemoglobin and biphosphoglycerate mutase deficiency, which result in tissue hypoxia and a secondary erythrocytosis. Alternatively, secondary polycythemia may be acquired and caused by increased amounts of EPO. This may be due to tissue hypoxia that may be central and caused by pulmonary or cardiac disease or high altitude, or local and caused by hypoxia in the kidney such as renal artery stenosis. EPO production may be pathologic and caused by EPO secreting tumors such as renal cell cancer, hepatocellular carcinoma, cerebellar hemangioblastoma, meningioma and parathyroid carcinoma/adenoma (see these terms). In addition EPO may be administered deliberately to produce erythrocytosis and enhance performance.
Diagnostic methods
Diagnosis is based on evidence of increased total red blood cells and normal to high serum EPO levels. Secondary causes of erythrocytosis must be diagnosed individually and will require a comprehensive history.
Differential diagnosis
Differential diagnoses include polycythemia vera and primary familial polycythemia (see these terms), which can be excluded on the basis of low EPO levels and the presence of a mutation in the JAK2 gene (9p24) for polycythemia vera.
Management and treatment
There is little evidence to guide management of congenital secondary polycythemia. Phlebotomy or venesection may be of benefit, particularly in patients at increased risk of thrombosis. A target hematocrit (Hct) of 50% may be the most practical. In patients with no specific contraindication, low-dose aspirin may be of benefit. In acquired cases of secondary polycythemia, management is based on treating the underlying condition.
Prognosis
Prognosis depends mainly on the associated disease in the acquired forms of secondary erythrocytosis and on the severity of thrombotic complications in the inherited forms such as in Chuvash erythrocytosis.

                            Last update: 
                            July 2010


                            - Expert reviewer(s): 
                            Pr Jean BRIERE