In this episode of Hospital Medicine Unplugged, we unpack mixed connective tissue disease—recognize the overlap syndrome hiding between lupus, scleroderma, and myositis, and aggressively monitor the pulmonary complications that drive morbidity and mortality.

MCTD is defined by high-titer anti-U1 RNP antibodies plus overlapping connective tissue disease features. The hallmark clues: • Raynaud phenomenon • Swollen hands • Sclerodactyly • Inflammatory arthritis • Myositis • GERD and esophageal dysmotility

Raynaud’s is often the earliest manifestation, and scleroderma-type findings help distinguish MCTD from lupus in anti-RNP–positive patients.

The major threat is pulmonary disease: • Interstitial lung disease (ILD) • Pulmonary arterial hypertension (PAH)

PAH remains the leading cause of death, making routine pulmonary surveillance essential: • Pulmonary function tests with DLCO • High-resolution CT when indicated • Echocardiography for PAH screening

Treatment depends on organ involvement: • Steroids for inflammatory flares • Mycophenolate, methotrexate, or cyclophosphamide for ILD and systemic disease • Rituximab for refractory cases

For MCTD-associated PAH: • Endothelin receptor antagonists • PDE-5 inhibitors • Prostacyclin pathway therapy • Immunosuppression may help more than in systemic sclerosis–associated PAH.

Key pearl: many patients achieve remission or stable disease, but up to one-quarter eventually evolve into a more defined connective tissue disease—most commonly systemic sclerosis or lupus.

We close with the system moves: don’t dismiss Raynaud’s plus swollen hands as “nonspecific,” screen aggressively for ILD and PAH, trend pulmonary function over time, and recognize that lung complications—not arthritis—determine long-term outcomes in MCTD.

The antibody may define the diagnosis, but the lungs define the prognosis.