Question

A 25-year-old female at the local hospital’s emergency department with symptoms of abdominal pain as well as severe vomiting and swelling of the legs and hands. She stated that she has had these symptoms on severe previous occasions. After ruling out appendicitis, the doctor orders a battery of tests including some for abnormalities of complement components. The following results were obtained: red and white blood cell count normal, total serum protein normal, CH50 decreased, alternative pathway function normal, C3 level normal and C4 and C2 levels decreased.

A. What symptoms lead to doctors to consider a possible complement abnormality?

B. What are the possible reasons for a decrease in both C4 and C2?

Answer 1

A. The patient developed the symptoms on several occasions. Also the symptom being swelling of legs and hands associated with abdominal pain and vomiting, doctors might have suspected hereditary angioneurotic edema, caused due to C1 esterase inhibitor deficiency. Another factor in favour of the diagnosis is the absence of urticaria. Urticaria along with the other symptoms usually suggests hypersensitivity to food or any other environmental factors.

B. C1 esterase inhibitor regulates the classical complement pathway by inhibiting the action of C1q by splitting C1qrs into C1rs and C1q. So, its absence causes overactivity of classical pathway. This lead to utilisation of excessive amounts of C4 and C2 and hence their serum levels fall.