Connective Tissue Disorders

The connective tissue disorders (CTDs) are systemic autoimmune diseases with autoantibodies, multi-organ involvement and a female predominance.

They are systemic lupus erythematosus (SLE), systemic sclerosis (SSc), the idiopathic inflammatory myopathies (IIMs), Sjogren's syndrome and mixed connective tissue disease (MCTD).

Antiphospholipid syndrome (APS) and the vasculitides are closely related. MSK symptoms (arthralgia, arthritis, myalgia, Raynaud's) are often the first complaint, and missing the systemic disease delays a diagnosis that can affect the kidneys, lungs and heart.

ANA is the screening test when a CTD is clinically suspected: sensitive but not specific, and never a blanket autoimmune screen.

CTDs share a loss of tolerance to self-antigens. In susceptible people, triggers such as UV light, infection, drugs and smoking lead to autoantibodies; immune complexes deposit in vessels, glomeruli, skin and serous membranes and activate complement.

• •SLE: immune-complex glomerulonephritis, non-erosive arthritis, serositis and cytopenias
• •SSc: vasculopathy, immune activation and fibrosis from excess collagen
• •Myositis: complement-mediated microangiopathy in dermatomyositis; antibody-driven muscle necrosis in immune-mediated necrotising myopathy
• •Sjogren's: lymphocytic destruction of the exocrine glands