The lung in mixed connective tissue disease

Mixed Connective Tissue Disease (MCTD) remains a controversial classificati on within the field of connective tissue diseases. Since its original descr iption in 1972 by Sharp et al, different alternative descriptions appear in the literature, such as "overlap syndrome" or "undifferentiated connective tissue disease." The diagnosis is based on the presence of overlapping sym ptoms of systemic lupus erythematosus (SLE), systemic sclerosis (SS), and p olymyositis (PM), and the detection of increased titers of anti-RNP (ribonu cleoprotein) antibody. Sharp et al thought that these patients had a distin ct rheumatological syndrome characterized by the absence of arthritis, rena l disease, and pulmonary involvement, as well as a favorable prognosis. Fur ther studies do not support this benign clinical course that spares the lun g. Pulmonary abnormalities have been described in 25-85% of MCTD patients. The pulmonary manifestations are similar in presentation and severity as se en in PSS, SLE, and PM. The most common presentations include interstitial lung disease, pleural effusions, and pulmonary arterial hypertension. Less common pulmonary presentations are diffuse alveolar hemorrhage with isolate d pulmonary capillaritis, rapidly progressive pulmonary arterial hypertensi on, small airway disease, pulmonary embolic disease, aspiration syndrome, a nd neuromuscular respiratory failure. The histologic descriptions of this l ung involvement are sparse. Nevertheless, the need for lung biopsy should b e determined on an individual basis and reserved for atypical presentations . Corticosteroids may be insufficient for the treatment of MCTD with pulmon ary involvement. Early cytotoxic therapy has been advocated for interstitia l lung disease and diffuse alveolar hemorrhage. This review will present th e diagnosis, clinical features, controversies, pulmonary involvement, thera py, and prognosis of this relatively new disease.