MKSAP Quiz: Follow-up for gonococcal arthritis
A 23-year-old woman undergoes follow-up after treatment for gonococcal arthritis. Following a physical exam, what is the most appropriate screening test to perform next?
A 23-year-old woman undergoes follow-up after treatment for gonococcal arthritis; she was treated with ceftriaxone. Her sister had meningococcal meningitis 2 years ago. The patient takes no medications.
On physical examination, she feels well with complete resolution of symptoms. Vital signs are normal, and the examination is unremarkable.
Which of the following is the most appropriate screening test to perform next?
A. CD4 lymphocyte subset
B. Serum IgA level
C. Total hemolytic complement (CH50) level
D. No additional testing
MKSAP Answer and Critique
The correct answer is C. Total hemolytic complement (CH50) level. This content is available to MKSAP 19 subscribers as Question 14 in the Infectious Disease section. More information about MKSAP is available online.
This patient should be evaluated for a defect in terminal complement level by testing the total hemolytic complement (CH50) level (Option C). She has a personal history of disseminated gonorrhea and a family history of meningococcemia. The terminal complement pathway includes C5 to C9, which together form the membrane attack complex, or MAC. The MAC plays a key role in host immunity against Neisseria species, and deficiency of a late complement component is associated with an up to 10,000-fold increased risk of meningococcal disease. Counterintuitively, although patients with terminal complement deficiencies are at increased risk of disseminated Neisseria infection, including meningococcal meningitis, these tend to be relatively mild and are rarely life-threatening. A personal history of recurrent Neisseria infection or a history of Neisseria infections among multiple family members is an indication to test for terminal complement deficiency. Some studies suggest up to a 20% prevalence of complement deficiency among patients with invasive meningococcal disease, justifying screening at the time of initial presentation, regardless of family history. In patients with a low CH50 level, more specialized testing can be performed to identify the specific protein deficiency. Patients with deficiencies in terminal complement levels should receive the conjugate and serogroup B meningococcal vaccines.
Idiopathic CD4 lymphopenia is associated with decreased T-cell function, and these patients are at risk for the same opportunistic infections seen in patients with HIV or AIDS, depending on the absolute level, but not Neisseria infections (Option A).
Selective IgA deficiency is the most common cause of primary immunodeficiency but is frequently asymptomatic (Option B). Recurrent sinus or pulmonary infections are the most common infectious complications of selective IgA deficiency, not Neisseria infections.
Not testing further would be inappropriate for this patient with a personal and family history of Neisseria infection (Option D). The identification of late complement deficiency has therapeutic implications because these patients should receive the conjugate and serogroup B meningococcal vaccines.
Key Points
- A personal history of recurrent Neisseria infection or a history of Neisseria infections among multiple family members is an indication to screen for terminal complement deficiency by measuring total hemolytic complement (CH50) level.
- Patients with terminal complement deficiency should receive the conjugate and serogroup B meningococcal vaccines.