Complement deficiencies — formative SAQs

SAQ 1 (10)

A previously well fourteen-year-old boy is admitted with his second episode of invasive meningococcal septicaemia in two years. He recovered fully from the first episode and has been entirely well between admissions, with no other significant infections and normal growth. His maternal uncle died of meningococcal meningitis in childhood. His C3 and C4 are normal, but the total haemolytic complement (CH50) is undetectable, and the AP50 is normal. [9] [10]

a) What is the most likely category of diagnosis, and which pathway is affected? Explain why the child is "otherwise well" despite the recurrent invasive infection. (3 marks) [9]

b) Justify why a normal C3 and C4 does not exclude this diagnosis, and name the correct first-line screen. (2 marks) [1] [2]

c) Outline the further investigations needed to confirm the specific deficiency and to plan family screening. (2 marks) [5]

d) Discuss the principles of long-term management, including prevention, family implications, and prognosis. (3 marks) [9] [10]

SAQ 2 (10)

A twelve-year-old girl presents to the emergency department with acute swelling of her tongue and floor of mouth that has developed over four hours. She has had similar episodes of subcutaneous and abdominal swelling since the age of eight, each lasting two to three days. There is no urticaria and no itch. Her father has a history of recurrent facial swelling. She was given intramuscular adrenaline, oral antihistamines and corticosteroids in the emergency department with no improvement. Her C4 is low. [7] [8]

a) What is the most likely diagnosis, and which protein is deficient? State two features that distinguish this from histamine-mediated (anaphylaxis) angioedema. (3 marks) [7]

b) Explain why adrenaline, antihistamines and corticosteroids are ineffective, and name the appropriate acute therapy. (3 marks) [8]

c) Outline the investigations needed to confirm the diagnosis, distinguishing type I from type II. (2 marks) [7] [8]

d) Describe a long-term management plan, including on-demand therapy, prophylaxis, and an action plan. (2 marks) [8]