Re: Pulmonary arterial hypertension in connective tissue diseases

Abstract

SIR, In their review of pulmonary arterial hypertension in connective tissue diseases, Kahler and Colleselli [1] discuss the epidemiology, pathophysiology, diagnostic tools and treatment options of this disease. However, in their first table, there seems to be confusion between the terms ‘pulmonary arterial hypertension’ and ‘pulmonary hypertension’. The revised World Health Organization classification of pulmonary hypertension [2, 3], is based upon the underlying pathophysiological processes involving the pulmonary blood vessels. Five classes are distinguished (Table 1). In the first ‘class, referred to as pulmonary arterial hypertension, the pulmonary arteries are the real site of pathology (hence the name of pulmonary arterial hypertension). The second class comprises those forms of pulmonary hypertension that afflict the veins and is hence called pulmonary venous hypertension. The third and fourth class consist of forms of pulmonary hypertension associated, respectively, with hypoxic lung disease and thromboembolic disease. The fifth class includes other rare causes of pulmonary hypertension and is referred to as the ‘miscellaneous’ class. So, in contrast to the terminology applied by Kahler and Colleselli in their first table (in which also class 2, 3 and 4 are referred to as pulmonary arterial hypertension), only the first class can truly be referred to as pulmonary arterial hypertension. For the clinician, it is important to realize that not all forms of pulmonary hypertension do represent pulmonary arterial hypertension. This distinction has also therapeutical consequences. Indeed, some drugs can be used to treat pulmonary arterial hypertension (e.g. vasodilators like calcium antagonists; prostaglandins; endothelin receptor antagonists), but not to treat the other forms of pulmonary hypertension. To illustrate this, vasodilator therapy, which may be helpful for patients with pulmonary arterial hypertension (class 1), could actually worsen the hypoxaemia in patients with class 3 pulmonary hypertension. Similarly, the non-appropriate use of vasodilators in patient with pulmonary venous hypertension (class 2) may actually increase signs of left heart failure.