Mixed Connective Tissue Disease: The Two Cases Representing the Range of this Illness

Mixed connective tissue disease (MCTD) is defined as a systemic rheumatic disease characterized by the presence of high titer anti-U1 ribonucleoprotein (U1 RNP) antibodies in combination with clinical features commonly seen in systemic lupus erythematosus (SLE), systemic sclerosis (SSc), rheumatoid arthritis (RA) and polymyositis (PM).

The annual incidence of MCTD is 1.9 per 100,000 adults. Any organ system can be involved in MCTD however four clinical features that suggest the presence of MCTD rather than another systemic rheumatic disease are Raynaud phenomenon with swollen hands or puffy fingers, absence of severe kidney disease and central nervous system (CNS) disease at first presentation generally, insidious onset of pulmonary hypertension and presence of autoantibodies anti-U1 ribonucleoprotein (U1 RNP), especially antibodies to the 68 kD protein. MCTD, although initially thought to be a disease with a benign course is not considered a valid argument at present. This connective tissue disorder can present with life-threating organ involvement with rapid progression of disease.

We report two cases of MCTD, one with mild disease and another with life-threatening illness, describing the range of severity at presentation of this disorder.