To the Editor:
In a recent issue of CHEST, Lee and Lepler (April 1999) rationally discussed the mimicking of hepatopulmonary syndrome (HPS) by the severe intrapulmonary shunting that is caused by carcinoid syndrome.
HPS is caused by hypoxemia in patients with chronic liver diseases in the absence of intrinsic lung disease, and so carcinoid-related intrapulmonary shunting and hypoxemia are not exactly the same as HPS. However, HPS may occur secondary to a functional right-to-left shunt because of intrapulmonary vascular dilatation. Thus, the shunting in that situation may mimic the pathogenesis of HPS in carcinoid syndrome. Furthermore, recent evidence suggests that nitric oxide (NO) is an important mediator of impaired oxygenation in patients with cirrhosis (ie, HPS).[4,5] The increased production of NO by metastatic carcinoid tumors in the lung may be another cause of extraordinary vasodilation and intrapulmonary shunting, resulting in severe hypoxemia in carcinoid syndrome.
Patients with carcinoid syndrome are known to produce the vasoconstrictor 5-hydroxytryptamine. However, NO, a major vasodilator, also may be produced in patients with carcinoid syndrome. Although carcinoid-related pulmonary shunting may be responsible for hypoxemia in the case of the patient reported by Lee and Lepler who has metastatic carcinoid tumors, the pathogenic mechanism of severe hypoxemia may not be simple in carcinoid syndrome. Because many neurohumoral vasoactive substances can be released by tumors, the complex regulatory mechanism may work in the lungs of the patients. Further analysis of vasodilators and vasoconstrictors may be important to elucidate the mechanism of hypoxemia in the carcinoid syndrome.
Shinji Teramoto, MD, FCCP Takeshi Matsuse, MD Yasuyoshi Ouchi, MD Tokyo University Hospital Tokyo, Japan
Correspondence to: Shinji Teramoto, MD, FCCP, Department of Geriatric Medicine, Tokyo University Hospital, 7-3-1 Hongo Bunkyo-ku, Tokyo, Japan 113-8655
 Lee DF, Lepler LS. Severe intrapulmonary shunting associated with metastatic carcinoid. Chest 1999; 115:1203-1206
 Krowka MJ, Cortese DA. Hepatopulmonary syndrome: current concepts in diagnosis and therapeutic considerations. Chest 1994; 105:1528-1537
 Whyte MK, Hughes JM, Peters AM, et al. Analysis of intrapuhnonary right to left shunt in the hepatopulmonary syndrome. J Hepatol 1998; 29:85-93
 Teramoto S, Matsuse T, Ouchi Y. Nitric oxide and impaired oxygenation before and after liver transplantation [letter]. Ann Intern Med 1999; 131:69
 Rolla G, Brussino L, Colagrande P, et al. Exhaled nitric oxide and oxygenation abnormality in hepatic cirrhosis. Hepatology 1997; 26:842-847
 Hansen MB, Dresner LS, Wait RB. Profile of neurohumoral agents on mesenteric and intestinal blood flow in health and disease. Physiol Res 1998; 47:307-327
COPYRIGHT 1999 American College of Chest Physicians
COPYRIGHT 2000 Gale Group