Grellier and colleagues [1] recently found that complete remission of polycythemia vera in a patient with acromegaly was achieved by the surgical cure of acromegaly, suggesting that growth hormone, insulin-like growth factor 1, or both may induce polycythemia. The authors did not consider another possible cause of polycythemia: The condition may occur in acromegaly as a result of hypoxemia related to sleep apnea.

Because obstructive sleep apnea occurs commonly in acromegaly [2], nocturnal sustained hypoxemia or periodical oxyhemoglobin desaturation is often found in acromegaly. Experimental data show that hypoxemia stimulates erythropoiesis. Furthermore, obstructive sleep apnea, hypoxic pulmonary vasoconstriction, and increased intrathoracic pressure associated with upper airway obstruction or resistance may cause impaired pulmonary and systemic circulation, contributing to the development or intensification of polycythemia.

The severity of obstructive sleep apnea in acromegaly was markedly improved by surgery [3] or the administration of a somatostatin analogue [4]. This finding suggests that the cure of acromegaly is accompanied by improvement of obstructive sleep apnea, resulting in the prevention of nocturnal hypoxemia. Moreover, the increased hematocrit and erythrocyte volumes in patients with obstructive sleep apnea were decreased when the apnea was successfully treated with nasal continuous positive airway pressure. This decrease was probably due to the improvement of hypoxia and hemodilution, indicating that the treatment of obstructive sleep apnea without any replacement of hormones is effective for polycythemia secondary to hypoxemia [5].

Taken together, the remission of polycythemia after successful surgical therapy in acromegaly may be partly explained by the improvement of obstructive sleep apnea and its related hypoxemia after therapy in addition to the actions of hormones.