Fusobacterium nucleatum brain and liver abscesses following sigmoid diverticulum perforation in an immunocompetent patient

We report a case of disseminated Fusobacterium nucleatum likely secondary to an undiagnosed perforated sigmoid diverticulum. A 50-year old male, (past history of COPD, schizophrenia and diverticulosis) presented with fever, seizures and progressive leg weakness over 4 days. Examination revealed left leg weakness and hepatomegaly. CT-brain showed bilateral supra-tentorial lesions with sulcal effacement; MRI findings were consistent with abscesses. Initial management included burr-hole drainage of 2 intra-cranial lesions and treatment with ceftriaxone and metronidazole. The patient defervesced post-operatively.

Blood cultures (day 1) and cerebral pus (day 3) grew Fusobacterium nucleatum after 5 days. HIV Ab/Ag negative. Subsequent imaging excluded endocarditis, intra-cardiac shunting and jugular vein thrombosis. CT revealed pulmonary emboli, liver abscess (68x46x42 mm, inaccessible to drainage) and localised sigmoid perforation. Later, the patient admitted to a 5-day period of severe self-limiting abdominal pain 2-weeks prior to admission, probably relating to sigmoid perforation.

The patient required further neurosurgical drainage (day 10) due to fluctuating consciousness; intra-operative samples were culture negative. Neurological improvement occurred during 4 weeks treatment. Total antibiotic duration will be determined by follow-up imaging.

Fusobacterium spp.are fastidious Gram-negative rods. Microscopy can differentiate the main pathogenic species showing tapered ends (F. nucleatum) or pleomorphic rods (F. necrophorum). Malignancy, diabetes and immunosuppression/HIV are associated, but none are present here. Presentations include abscesses, bacteraemia, thrombophlebitis, osteomyelitis and endocarditis. This case highlights the need for early sampling, careful history regarding source, covering at least 2-4 weeks preceding presentation, and demonstrates paradoxical deterioration after antibiotics and drainage, likely due to post-treatment inflammatory reaction.