Two cases of portal vein thrombosis associated with Fusobacterium bacteraemia

This report presents two cases of Fusobacterium bacteraemia associated with portal vein thrombosis. A 63-year-old man with a history of hypercholesterolaemia and nephrolithiasis was admitted to the hospital with fever and abdominal pain. A computed tomography (CT) scan revealed thrombosis of the posterior right portal vein. Blood cultures were positive for Fusobacterium nucleatum. The second case was a 53-year-old man with alcoholic steatohepatitis admitted with fever, chills and abdominal pain. A CT scan revealed right portal vein thrombosis and Fusobacterium necrophorum was isolated from his blood cultures. Both patients were successfully treated with intravenous ertapenem 1 g day for 4 weeks with resolution of symptoms. These case reports underscore the importance of considering the diagnosis of portal vein thrombosis in patients with Fusobacterium bacteraemia of unclear aetiology.


Introduction
Both Fusobacterium necrophorum and Fusobacterium nucleatum cause bacteraemia in humans (Henry et al., 1983).While Lemierre's syndrome is classically associated with F. necrophorum, there have been cases attributed to F. nucleatum (Williams et al., 2003).Few cases of Fusobacterium bacteraemia in association with venous thrombus disease caudal to the head and neck have been described.This report presents two cases of portal vein thrombosis associated with Fusobacterium bacteraemia.

Case reports
Case 1 A 63-year-old man with a history of mastocytosis, hypercholesterolaemia, nephrolithiasis and squamous cell skin cancer was admitted to hospital with fever and abdominal pain.The pain started 3 weeks prior to admission, lasted 48 h and resolved spontaneously.The day before the patient was admitted, he developed shaking chills and diaphoresis.His other symptoms included diffuse myalgias, arthralgias and bilateral lower-quadrant abdominal pain associated with one episode of bilious vomiting.
A computed tomography (CT) scan revealed complete thrombosis of the posterior right portal vein (Fig. 1).Bacterial growth in BD Bactec liquid media was established after 61 h incubation.Gram staining revealed an indolepositive, Gram-negative bacillus.F. nucleatum was isolated using CDC anaerobe 5 % sheep blood agar, and biochemical identification was performed with the Remel IDS system for anaerobes (RapID; Remel Microbiology Products).The patient was initially treated with intravenous (IV) piperacillin-tazobactam 3.375 g every 6 h, followed by 1 g day -1 ertapenem IV for a total of 4 weeks.He was also anticoagulated with warfarin, with complete resolution of his symptoms.

Case 2
A 53-year-old man with a history of gastroesophageal reflux disease, obstructive sleep apnoea, alcoholic steatohepatitis, obesity and hypercholesterolaemia was admitted complaining of fever, chills and abdominal pain for 1 week.Prior to the patient's presentation at the hospital, he had taken levofloxacin prescribed by his physician, without resolution of his symptoms.
A CT scan revealed thrombosis of the right portal vein (Fig. 2).After 24 h incubation, F. necrophorum was isolated from the anaerobic sample in a fashion similar to that described in case 1.The patient's symptoms resolved following treatment with 1 g day -1 ertapenem IV for a total of 4 weeks.He was also anticoagulated with warfarin.

Discussion
Fusobacterium species are obligate, anaerobic, non-sporeforming Gram-negative bacilli.F. necrophorum and F. nucleatum are a normal part of the oropharyngeal flora and are not usually invasive.Of the 13 species in this genus, F. necrophorum is classically associated with internal jugular vein thrombosis in the form of Lemierre's syndrome.However, cases caused by F. nucleatum have been described (Williams et al., 2003).
While F. necrophorum is known to induce platelet aggregation, thrombotic events outside of the head and neck are rare (Forrester et al., 1985;Horose et al., 1992).When they do occur, they are mainly seen in elderly patients and mortality can approach 25 % (Hagelskjaer & Prag, 2000).Portal vein thrombosis in association with both F. necrophorum and F. nucleatum has been reported (Bultink et al., 1999;Hamidi et al., 2008;Redford et al., 2005).The source of bacteraemia in these patients is not always evident, and it has been suggested that in cases of Fusobacterium bacteraemia of unknown origin, portal vein thrombosis should be ruled out (Hamidi et al., 2008).
Fusobacterium species are normally susceptible to penicillin, clindamycin, carbapenems and metronidazole (Garrett & Onderdonk, 2010).Interestingly, the F. nucleatum species isolated from the second case described was resistant to metronidazole.Routine sensitivity testing of anaerobic isolates is not performed in all laboratories, but might be worthwhile.Antimicrobial therapy is generally recommended for several weeks for the treatment of Lemierre's syndrome (Hagelskjaer et al., 1998).In addition to 4 weeks of parenteral antimicrobial therapy, we chose to anticoagulate our patients with warfarin, as this has been shown to increase vessel recanalization (Sheen et al., 2000).
In conclusion, this report describes two cases of Fusobacterium bacteraemia in association with portal vein thrombosis.Both patients responded well to antimicrobial therapy and anticoagulation.A diagnosis of portal vein thrombosis should be considered in patients with Fusobacterium bacteraemia of unclear aetiology.

Fig. 1 .
Fig. 1.CT scan showing thrombosis of the right posterior portal vein in case 1.