C1 inhibitor deficiency simulating systemic lupus erythematosus.

A 48-year-old Japanese woman with systemic lupus erythematosus-like lesions of the skin and lips was found to have hereditary angio-oedema. Complement studies revealed low CH50, C1q, C4 and C1 inhibitor levels, with normal C3 and C5 levels. Dramatic clinical improvement followed fresh normal human blood transfusion and systemic betamethasone administration, while the deficient complement component levels were unchanged.