Invasive Non-groupable Meningococcal Disease Complicated by Brain Abscess Revealing C6 Complement Deficiency in a Young Adult.

A 21-year-old man presented with sickle cell trait with septic shock, altered mental status, and respiratory failure. Blood cultures grew non-groupable Neisseria meningitidis. His course was complicated by consumptive coagulopathy, stress-induced cardiomyopathy, and a 2.8×1.2 cm rim-enhancing brain lesion concerning for abscess. Transesophageal echocardiography showed no endocarditis, supporting hematogenous seeding. The abscess resolved with prolonged intravenous ceftriaxone. Outpatient immunologic evaluation revealed low CH50 and C6 complement deficiency, prompting vaccinations and long-term penicillin prophylaxis. This case highlights brain abscess as a rare complication of meningococcal disease and underscores the importance of evaluating for complement deficiency in atypical presentations.