Background

Acute kidney injury occurs in up to half of all septic patients [1, 2] and carries a significant risk of end-stage kidney disease with the frequent requirement of chronic renal replacement therapy [3].

Acute renal cortical necrosis (ARCN) is an uncommon form of acute kidney injury in states of shock and is the result of direct toxic damage to the glomerular endothelium, as well as microthrombi resulting from sepsis [4, 5]. In contrast-enhanced computed tomography (CT), the non-perfusion of the renal cortices due to necrosis results in a non-enhancement in contrast to adequately enhancing renal medullae mimicking a retrograde renography [4]. This CT finding is pathognomonic for ARCN and usually results in permanent kidney injury [6].

Capnocytophaga canimorsus is a slow-growing, capnophilic, facultative anaerobic Gram-negative rod. It was first described in 1977 as a dysgonic fermenter 2 (DF-2), and in 1989 taxonomically classified as C. canimorsus [7, 8]. Although C. canimorus is part of the normal oral flora in up to two-thirds of cats and dogs [9], only three serovars (A-C) cause invasive disease in humans [10]. Its primary mode of transmission to humans is by animal bites, but it can even be transmitted by licks of damaged skin and scratches [11, 12]. Immunocompromised patients are particularly vulnerable to fulminant C. canimorsus sepsis, but also immunocompetent patients may experience severe clinical courses with high morbidity and mortality [12, 13]. In the sub-group of immunocompromised patients, asplenic patients and patients with alcoholism are particularly vulnerable to C. canimorus. In two scoping reviews of published C. canimorsus cases, the most frequent clinical entities were sepsis complicated by septic shock, meningitis, multiple organ failure, peripheral gangrene, and DIC with a high case fatality rate of up to 56% [12, 13] Table 1 gives an overview of the variety of possible clinical presentations of C.canimorsus.

Table 1 Selection of clinical presentations of C.canimorsus infections
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Case report

We recently treated a 44-year-old Caucasian woman who presented to a regional hospital with abdominal complaints and pyrexia for the last 24 h. Past medical history revealed an allogeneic stem cell transplantation 12 years ago due to acute lymphoblastic leukemia, which was in full remission. At the time of infection, the patient had no ongoing immunosuppressive treatment. However, there was evidence of transplantation related functional asplenia by the repetitive detection of Howell-Jolly bodies in peripheral blood smears and a CT-radiographic small, atrophic spleen with a length of 3.8 cm. Four days prior to presentation, the patient was bitten by her dog on the index finger but did not seek medical attendance because there were no signs of infection. Solely, a small sensory deficit of the affected finger was reported. The patient then presented with sudden abdominal cramps, bilious vomiting, epigastric pain, pyrexia up to 40 °C and shivering.

Upon admission to the regional hospital, the clinical examination revealed a tachycardic, hypotensive, tachypneic, and febrile patient with a tense abdomen and two small skin lesions without any signs of infection on her index finger. An abdominal ultrasound showed a dilated small-bowel with pendular peristalsis, ascites, and gallbladder wall thickening.

For suspected abdominal infection, an empiric antibiotic treatment with piperacillin/tazobactam was started after collecting blood cultures. Hence, the patient was immediately transferred to our tertiary teaching hospital.

Our hospital’s initial laboratory work-up revealed signs of infection, coagulopathy, acute kidney injury, and severe lactic acidosis with normal liver/pancreatic parameters (Table 2). The contrast-enhanced CT scan showed a reactive wall enhancement of the gallbladder, ascites, and bilateral ARCN by the “reverse rim sign” (Fig. 1). Due to a high suspicion of cholecystitis causing abdominal sepsis, the patient underwent open cholecystectomy. However, interoperative findings and histological examination did not support this diagnosis.

Table 2 Laboratory results on admission
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Fig. 1
figure 1

Contrast-enhanced abdominal CT scan, with a bilateral hypo-perfused renal cortex and an adequately perfused renal medulla = “reverse rim sign”. This finding is pathognomonic for acute renal cortical necrosis

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Postoperatively, the disseminated intravascular coagulation (DIC) worsened, and transfusion of coagulation factors was inevitable, calling for liver packing due to uncontrolled bleeding from the surgical site. Further clinical manifestations of the DIC were profuse bleeding from puncture sites and drainages as well as purpura fulminans. The clinical course was further complicated by a critical hemodynamic instability with profound hypotension and septic cardiomyopathy requiring inotropes. Shortly after admission to intensive care, the laboratory reported identification of rod-shaped bacteria directly from the first peripheral blood smear done in the regional hospital (Fig. 2), suggesting a high pathogen load. Later, blood cultures also revealed Gram-negative rods in Gram staining, which did not grow using standard culture conditions. Together with the clinical information about a dog bite, this raised suspicion for C. canimorsus. Bacterial growth was finally achieved on chocolate agar incubated under micro-aerophilic conditions and identified as C. canimorsus by MALDI-TOF mass spectrometry. C. canimorus was sensitive to penicillin (MIC = 0.004) and ceftriaxone (MIC = 0.023). The clinical course was further complicated by permanent hemodialysis and extensive acral necrosis, requiring amputation of several fingers and both thighs. After hemodynamic stabilization and prolonged weaning, the patient could be transferred to the ward after 6 weeks of intensive care and is currently making good progress in rehabilitation.

Fig. 2
figure 2

Peripheral blood smear with May-Grünwald-Giemsa stain. Polymorphonuclear leukocyte with intracellular rod-shaped bacteria (black arrow ); image kindly provided by Health Center Fricktal, Rheinfelden, Switzerland)

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Discussion and conclusions

To our knowledge, this is the first published case of a C. canimorsus infection complicated by bilateral ARCN with the rare CT-finding of a “reverse rim sign” (Fig. 1) [4,5,6] C. canimorsus associated disseminated intravascular coagulation may lead to microthrombi in renal glomeruli resulting in permanent kidney failure. C. canimorsus is usually susceptible to all beta-lactam antibiotics (including penicillin) and clindamycin. International guidelines suggest amoxicillin-clavulanate as prophylactic therapy after a dog bite [26]. The adjunction of beta-lactamase inhibitors seems reasonable, as beta-lactamases have been isolated in Capnocytophaga spp [27].

Concerning this rare pathogen, there is mainly anecdotal evidence in the form of case reports [7,8,9,10,11] and scoping reviews [12, 13] of published cases implicating a significant publication bias. Well-designed prospective research is warranted to gain further knowledge regarding this chameleon-like disease.

In conclusion, immunocompromised patients should be informed about the potential severe sequelae of animal bites and instructed to seek immediate medical advice, although bite wounds are minor or initial symptoms might be lacking. As proposed in the literature, physicians must initiate a pre-emptive antibiotic treatment in any wounds inflicted by cats and dogs in asplenic patients and should strongly consider pre-emptive treatment in other forms of immunosuppression (e.g., alcoholism) also [26, 28]. However, if ARCN is a new pathophysiologic entity associated with C.canimorsus infections or a result of the symptomatic DIC cannot be obtained from a single case.