Complement deficiency are rarely congenital, seen more commonly as acquired defects due to —
a) Deficient production e.g. in newborns, PEM and chronic liver diseases,
b) Defective function e.g. in sickle cell disease,
c) Increased consumption or loss e.g. in septicemia, bums, SLE and nephrotic syndrome.
Clinically, complement deficiency cases present with recurrent pyogenic or neisserial infections, frequently associated with immune- complex disorders (lupus-like illness) and vasculitis syndromes.
Diagnosis is established by assessing CH50 activity with control or direct C3-C4 immunoassays. Genetic workup is needed to identify inherited complement disorders, all of whom are autosomal recessive except properdin deficiency (X-linked).
Management is non-specific, as complement replacement therapy is not available and includes prolonged antibiotic therapy during infections and immunization against capsular organisms like pneumococci or meningococci.
Hereditary angioedema is an important autosomal dominant defect of C1 inhibitor deficiency with unrestricted complement activity causing complement deficiency.
Clinically, these cases presents with recurrent self-limiting episodes of non- pitting edema due to vasodilatory effect of kinins released by uncontrolled breakdown of C4 & C2. Each attack lasts for 2-3 days and may be fatal.
Antihistaminics and steroids are not effective and acute attacks need to be treated with supportive measures like tracheostomy for complement deficiency. Prophylactic oral attenuated androgen (stanozolol) therapy may be useful in frequently recurrent cases.