Capnocytophaga canimorsus septicaemia in an asplenic patient with systemic lupus erythematosus

Abstract

Asplenic patients are highly susceptible to infections with encapsulated bacteria such as Capnocytophaga canimorsus, a gram negative bacillus which is a commensal organism in cat and dog saliva. We describe the first case of septic shock due to C canimorsus infection occurring in a 51-year-old woman with functional asplenism related to systemic lupus erythematosus with antiphospholipid antibodies. Because of the potential severity of this infection, physicians have to be aware of its occurrence in lupus patients.

BACKGROUND

Capnocytophaga canimorsus is a gram negative bacillus and commensal bacterium of the canine oral flora, and has been repeatedly isolated since 1976. C canimorsus infections in human are mostly transmitted by bites or scratches from dogs or cats and remain largely underestimated. Severe infections commonly affect immunocompromised subjects.¹ We report herein the first case of C canimorsus septicaemia occurring in a systemic lupus erythematosus (SLE) patient with functional asplenism.

CASE PRESENTATION

A 51-year-old woman with SLE was hospitalised for septic shock with diarrhoea, abdominal pain, vomiting, myalgia and recent recurrent epistaxia. The patient recalled a domestic dog bite she received 4 days before symptoms appeared and from which a chin scar remained. SLE was diagnosed in 1993 (4 American College of Rheumatology (ACR) 1982 positive criteria). Complications included a Liebman–Sachs aortic endocarditis in 2002, and a severe pulmonary arterial hypertension in 2003 (median pulmonary arterial pressure of 42 mm Hg) requiring steroids, bosentan, and cyclophosphamide bolus relayed by oral methotrexate. In 2005, a nephritic syndrome with renal insufficiency appeared and was related to a renal vasculitis on kidney biopsy, leading to one course of rituximab therapy which proved effective. Thereafter, all other immunosuppressive treatments were discontinued. Search for antiphospholipid autoantibodies revealed positive anticardiolipin antibodies of IgM isotype and lupus anticoagulant. Mild chronic thrombocytosis (450–500×10⁹/l) was also noticed and was considered to be linked to functional asplenism owing to the presence of Howell–Jolly bodies on the blood smear. For this, she received pneumococcal vaccination. Her usual treatment was salicylic acid, perindopril, bosentan and alendronate. At physical examination, a systolic heart murmur, limb petechial purpura, and palatal petechiae were noticed.

INVESTIGATIONS

Biological investigations revealed: normochromic and normocytic anaemia (haemoglobin to 11.4 g/dl), hyperleucocytosis to 12.3×10⁹/l, severe thrombocytopenia to 5×10⁹/l, a high creatininaemia to 1500 µmol/l and urea to 45 mmol/l, C reactive protein >300 mg/l, liver cytolysis, and icteric cholestasis. Biological signs of disseminated intravascular coagulation were noted in regard to the low prothrombin time, low fibrinogen concentration and liver cofactors consumption. Three days after admission, blood cultures isolated Capnocytophaga species sensitive to amoxicillin, identified as C canimorsus by 16S ribosomal RNA amplification. Abdominal and renal echography and thoracoabdominal computed tomography (CT) scanner only revealed a splenic atrophy.

TREATMENT

Haemodynamic status was stabilised by salted serum infusions and epinephrine, and non-invasive ventilation was initiated for acute respiratory distress syndrome. Intravenous antibiotic treatment with ceftriaxone and ciprofloxacin was initially administered then was switched to amoxicillin 6 g daily for 15 days.

OUTCOME AND FOLLOW-UP

We decided on a diagnosis of septic shock with multiple organ failure due to C canimorsus infection originating from a dog bite. The patient’s outcome was good after 30 days of hospitalisation, with complete physical and biological recovery to her previous state. No evidence of lupus flare was found during the hospitalisation.

DISCUSSION

C canimorsus infection remains a rare cause of fulminating infection, and usually affects males of 50 years or older. Clinical features vary from a localised but rare skin or ocular infection to, in most cases, a systemic infection with a febrile flu-like syndrome, with digestive signs, as observed here, which can sometimes mimic a surgical acute abdominal syndrome and lead to laparotomies.^1,2 Respiratory distress syndrome and acute renal failure, also observed here, are reported in the literature, as well as meningitis, brain abscess, endocarditis, and arthritis. Septic shock state is associated to a disseminated intravascular coagulation syndrome in 30% of the cases.¹ C canimorsus systemic infections are fatal in 30% of cases.¹ Bite wounds must be treated by an early local decontamination, with surgical exploration when necessary. Moreover, preventive antibiotic treatment targeted at C canimorsus must be prescribed for fragile patients, all patients with a deep bite wound, and those seen up to 6 h after the bite. Many authors use amoxicillin combined with clavulanic acid for preventive as well as curative treatment.¹

C canimorsus virulence is weak in healthy subjects and host susceptibility to its infection is dependant on complement lytic response and reticuloendothelial phagocytosis,³ which are both impaired in immunocompromised patients. As a consequence, sepsis is mostly associated with an immune deficiency such as asplenia in 33% of cases, chronic alcoholism in 24%, and other immunocompromised conditions in 5% of cases.¹ Functional asplenism was firstly reported in 1982 in five of 70 patients with SLE.⁴ In a further study 1 year later, functional asplenia was observed in 2/44 SLE patients (4.6%).⁵ After the discovery of the antiphospholipid syndrome, functional asplenia has been reported to be mostly associated with the presence of antiphospholipid antibodies, or fully developed antiphospholipid syndrome in a few SLE patients as a consequence of an autosplenectomy.^6–8 The presence of antiphospholipid antibodies (as observed in our patient), or fully developed antiphospholipids syndrome, support the view that multiple thrombotic events within the splenic microvasculature could be involved in its pathogenesis.⁸ Other hypotheses have included splenic vasculitis with silent infarct.⁸ Although functional asplenia is a rare event in SLE, it predisposes to severe septic complications such as pneumococcal and salmonella sepsis.⁹ To our knowledge, C canimorsus infection in SLE patients has not been previously published; however, we considered asplenia related to SLE with antiphospholipid antibodies as a predisposing condition of this infection.

Because of the potential severity of C canimorsus infection, physicians have to be aware of its occurrence, especially in immunocompromised patients. As highlighted in our observation, SLE patients must be considered at risk of infection due to functional but rare asplenia and/or immunosuppressive drugs administered as SLE therapy.

LEARNING POINTS

• Capnocytophaga canimorsus infection in asplenic or immunocompromised patients is life threatening.

• Physicians must be aware of C canimorsus infection after a dog or cat bite, which should be inquired about.

• Lupus patients should be considered at risk for C canimorsus infection.