EXPERIMENTAL AND CLINICAL TRANSPLANTATION

Rhodococcus equi is a well-recognized pathogen in veterinary medicine that can also affect immuno-compromised human subjects. The most common clinical features in humans include necrotizing pneumonia with subacute pulmonary disease, progressive cough, chest pain and fever. We report a case of a 49-year-old kidney transplant patient who developed a Rhodococcus equi infection characterized by multiple abscesses of the soft tissues and muscles without any respiratory manifestation. Combining specific antibiotic therapy and surgical management of the abscesses without immunosuppression discontinuation led to a complete recovery of both patient and graft.

Key words : Abscess, Graft, Antibiotic

Rhodococcus equi is a veterinary pathogen that usually affects domestic animals, but in rare instances it can also infect immunocompromised human beings. Case reports have been described in immuno-suppressed patients having hematologic diseases, AIDS, and solid-organ transplants.¹ The typical clinical picture of the infection in humans is characterized by respiratory symptoms with cough, chest pain, high fever, and pathognomonic radiographic signs. In this report, we describe an unusual case of an R. equi infection that occurred in a kidney transplant patient, in whom the main clinical signs were multiple abscesses of the soft tissue and subcutaneous tissue.

A 49-year-old kidney transplant patient was admitted to our center for fever associated with limb pain. In his recent history he denied any exposure to any particular risk factors, except for having spent 2 days at a horse exhibition the week before. He received the kidney transplant 5 months earlier, and was currently under immunosuppression therapy with steroids (prednisone 5 mg daily), tacrolimus, and mycophenolate mofetil. On the first physical examination, he was febrile and presented with multiple nodules located in the soft and subcutaneous tissues of the chest and left leg. Macroscopically each nodule was 3 to 4 cm in diameter, warm, reddened, painful on palpation and with an area of erythema of the surrounding skin. Histologic examination of one of the lesions revealed a microscopic picture of abscess. In the following days nodules showed a migrant progression appearing in other various sites of the body (right leg and both arms). Radiologic evaluation (ultrasound, computerized tomography, and scintigraphy) confirmed the picture of subcutaneous abscesses without any lung involvement or respiratory abnormalities (Figure 1). A subsequent magnetic resonance image of the legs confirmed the presence of subcutaneous lesions with an abscess involvement of the right soleus muscle. Laboratory examinations showed a high white blood count (14.3 × 10⁹/L), with stable renal function and normal immunosuppressive levels. While waiting for the result of the culture examinations, we started a broad-spectrum antibiotic therapy with metronidazole, cefepime, tigecycline, and piperacillin/tazobactam.

After 1 week, the blood culture results were negative, while the microbiologic examination of the liquid drained from 1 of the subcutaneous abscesses revealed an R. equi infection. Based on the specific antibiogram, a target antibiotic therapy with intravenous ciprofloxacin and vancomycin was initiated. Simultaneously, we decided to perform multiple surgical drainages of the largest abscesses of the legs and thoracic wall. Immunosuppression therapy was never changed or discontinued. The patient showed a progressive clinical improvement until complete resolution after 3 months of continuous antibiotic therapy and multiple surgical procedures. The patient was discharged and remains in good health, with stable renal function and no signs of infection recurrence after 36 months of follow-up.

R. equi (previously known as Corynebacterium equi) is a nonmotile Gram-positive aerobic bacterium that looks coccoid in solid media and tissue or bacillary in liquid media.² The organism is a well-known pathogen in veterinary medicine, affecting young horses with purulent bronchopneumonia, abscesses and suppurative lymphadenitis.³ The surface soil of horse farms typically have high concentrations of R. equi and the most frequent route of transmission is the inhalation of infected aerosols and dust particles.³ Rarely, R. equi can also infect humans, especially immunosuppressed patients with hematologic diseases, AIDS, or solid-organ transplants. Infection in humans follows the same route as in animals, and is strongly associated with exposure to farming environments and domesticated animals such as horses.⁴ The most common clinical features in humans are characterized by necrotizing pneumonia with a subacute pulmonary disease, progressive cough, chest pain, and fever. Chest computerized tomography scans usually show pulmonary infiltrates with cavitation, pleural based nodules and swollen lymph nodes. In approximately 20% of cases osteomyelitis, purulent pericarditis, subcutaneous abscesses, and multiple brain abscesses also were described.⁵ A recent review of the literature has reported a total of 41 cases of R. equi infection in solid-organ transplant patients, 24 of which occurred in kidney transplants, 7 in hearts, 3 in livers and 6 in others.⁶ In contrast to the majority of cases in the literature, our patient did not express any pulmonary involvement, instead showing only soft tissue and subcutaneous multiple abscesses. In our case the blood cultures always remained negative and the R. equi was isolated to the abscess liquid specimens only. Nevertheless, the different exacerbations of multiple migrant abscesses that characterized the course of the disease could be related to bacteremic peaks.

The standard treatment of choice for R. equi infection is still controversial with respect to both type of antibiotic and duration of therapy. Different authors have reported that R. equi is usually susceptible in vitro to macrolides, rifampicin, aminoglycosides, fluoroquinolones, glycopeptides, and imipenem,⁷ but combined antibiotic therapy based on susceptibility testing remains the mainstay of treatment in clinical practice.⁸ In cases such as our patient, characterized by multiabscess lesions, we think that the additional surgical treatments for drainage are recommended, while immuno-suppression therapy should be strictly monitored but not necessarily discontinued.

Volume: 14 Issue: 6 December 2016

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