Undifferentiated Connective Tissue Disease (UCTD)
describes a syndrome in which a patient has some of the clinical
features of one of the systemic autoimmune rheumatic diseases and a
positive ANA but do not meet criteria for a more specific diagnosis.
Suggested classification criteria for UCTD:
Signs and symptoms of a CTD, but not fulfilling the criteria for any of the defined CTDs for at least 3 years,
Presence of ANAs on two different occasions.
The majority of patients with UCTD are female (80% to 95%) with disease onset during the fourth decade (30 to 40 years old).
The most frequent manifestations of UCTD are arthralgias/arthritis, Raynaud’s phenomenon, mucocutaneous manifestations, and sicca symptoms. Major organ involvement is rare. Most patients (up to 90%) are ANA positive but lack specific autoantibodies against Sm, dsDNA, and centromere. Some patients have anti-SSA antibodies, which correlate with sicca symptoms and mucocutaneous lesions; others have low titer anti-RNP antibodies, which correlate with Raynaud’s phenomenon and arthritis.
Certain combinations of features are predictive for development of a defined CTD: UCTD patients with fever, serositis, and/or anti-Sm or anti-dsDNA antibodies are more likely to develop SLE; patients with Raynaud’s phenomenon, abnormal nailfold capillaries, and nucleolar ANA develop scleroderma; patients with xerostomia and anti-SSA/SSB antibodies develop Sjögren’s syndrome; patients with polyarthritis and high titer anti-U1-RNP develop MCTD; and patients with myositis and antisynthetase antibodies develop myositis–interstitial lung disease overlap. Notably, some patients with UCTD may have severe involvement in only one major organ. This is particularly likely with lung involvement (lung-dominant connective tissue disease).