Musculoskeletal disorders 

SLE is a relapsing multisystem autoimmune disease of mainly young women, with fever, arthritis, malar rash, nephritis, serositis, cytopenias and neurological features, and ANA, anti-dsDNA and low complement. All patients take hydroxychloroquine, with steroids, azathioprine, methotrexate, mycophenolate, cyclophosphamide or rituximab according to organ involvement; neonatal lupus comes from maternal anti-Ro/La antibodies.

Systemic sclerosis is autoimmune fibrosis and vasculopathy causing skin thickening, Raynaud's, digital ulcers, reflux, interstitial lung disease, pulmonary hypertension and scleroderma renal crisis. Keep warm, use nifedipine for Raynaud's, PPIs for reflux, cyclophosphamide or mycophenolate for ILD, and an ACE inhibitor urgently for renal crisis.

Sjögren's syndrome is autoimmune destruction of salivary and tear glands causing dry eyes and mouth, parotid swelling and extra-glandular disease, alone or with RA, SLE or HIV, and a lymphoma risk. Use artificial tears and saliva, dental care, pilocarpine for dry mouth, hydroxychloroquine for fatigue and joints, and steroids or immunosuppressants for systemic involvement.

Dermatomyositis and polymyositis are inflammatory myopathies with symmetric proximal muscle weakness and raised CK; dermatomyositis adds heliotrope rash and Gottron's papules and carries a cancer risk. Treat with high-dose prednisone plus methotrexate, azathioprine, hydroxychloroquine (skin) or cyclophosphamide, with IVIG or rituximab for refractory disease and physiotherapy.

Mixed connective tissue disease is an overlap of SLE, systemic sclerosis and polymyositis features with high anti-U1 RNP antibodies, often starting with Raynaud's. Treat with prednisone and steroid-sparing agents (methotrexate, azathioprine, hydroxychloroquine or cyclophosphamide) and monitor for lung and heart complications.