Diffuse smooth muscle proliferation of the lungs with severe pulmonary hypertension.

We describe the second example of a distinctive clinicopathologic syndrome of severe pulmonary hypertension and interstitial lung disease caused by diffuse smooth muscle proliferation of the lungs (DSMPL) occurring in a 44-year-old man of normal intelligence with no cutaneous or neurological lesions. The smooth muscle proliferation involved the walls of bronchioles, alveoli, small pulmonary arteries, and pulmonary veins. DSMPL is distinct from pulmonary lymphangioleiomyomatosis and tuberous sclerosis, and does not appear to be neoplastic or reactive. The lesions are probably best regarded as multiple hamartomas or "native benign nodular smooth muscle proliferations."