Pulmonary involvement in
mixed connective tissue disease (
MCTD) is common, frequently severe, and is often clinically inapparent and variably responsive to
corticosteroid/
cyclophosphamide treatment. Serial pulmonary evaluation of patients with
MCTD is important, since deterioration, as in the diffusing capacity over time, may alert the physician to the need for more invasive evaluation. Patients with a greater degree of overlap in rheumatological symptoms with an
element of
systemic sclerosis (PSS) may later develop severe disease. Nailfold capillary microscopy also may help in determining which patients will develop severe pulmonary involvement. Significant
pulmonary hypertension occurs and cannot be accurately predicted on the basis of history, physical examination, pulmonary function tests,
gallium scanning, or exercise testing. The characteristic pathological finding was intimal proliferation with medial muscular
hypertrophy in the pulmonary arterioles. In contrast, pulmonary interstitial abnormalities were minimal, suggesting the proliferative vascular lesions are more closely associated with
pulmonary hypertension in
MCTD. Some patients develop rapidly progressive disease with varying response to
corticosteroid and
cytotoxic agents. More commonly, however,
MCTD patients with long-term disabling disease, including pulmonary dysfunction, have had significant improvement with
steroid and/or
cyclophosphamide treatment, and clinical remission has occurred in 38% of the patients in this series.