Infection is an important complication of cerebrospinal fluid (CSF) shunting procedures. Propionibacterium acnes shunt infections are typically indolent, with vague clinical and laboratory findings and can be easily overlooked.1–3P. acnes identification is essential because antibiotics alone are not sufficient to eradicate the organism from the ventricular system, and total shunt replacement is recommended.
This is a 9 year-old girl who had been born prematurely and who has had a ventriculo-peritoneal (VP) shunt since 2 months old placed because of hydrocephalus secondary to neonatal meningitis. VP shunt was last revised at 8 years of age. A year later, she had her peritoneal catheter replaced because of an abdominal pseudocyst. At that time, CSF cultures were sterile.
Four weeks later, she presented with progressive colicky lower quadrant abdominal pain.
On admission, the child was unwell, temperature was 37.8°C and cutaneous erythema was present along the subcutaneous tract of the VP shunt (Figure 1). There was no evidence of neurologic deficit or altered mental status. Laboratory studies showed a peripheral white blood cell count of 8600 cells/mm, with 78% neutrophils and C-reactive protein of 9.2 mg/dL. Abdominal ultrasound showed the presence of echogenic intraperitoneal fluid around the catheter tip. The brain computed tomography was normal. The peritoneal catheter was externalized, and CSF analysis showed 25 cells, mostly polymorphonuclear, protein of 28 mg/dL and glucose 61 mg/dL. She was given ceftriaxone and vancomycin, with a diagnosis of a probable shunt infection. Her symptoms improved on the second day of treatment, and the C-reactive protein declined. CSF Gram stain and culture were negative. Blood cultures were sterile.
After 10 days of hospitalization, she again had fever, and the C-reactive protein increased to 4.6 mg/dL. Antibiotics were changed to vancomycin, meropenem and rifampin because of the possibility of an externalized shunt nosocomial infection and the presence of a biofilm. Repeated CSF and blood cultures were negative. The study of 16S ribosomal RNA polymerase chain reaction (PCR) in the first CSF sample identified P. acnes. The VP shunt was replaced by a new shunt impregnated with clindamycin and rifampin after 7 days of triple antibiotic therapy. Patient was discharged 1 week later without further complications.
We describe a case of VP shunt infection by P. acnes.
Infection remains an important complication of CSF shunting procedures in both adults and children, and most occur within few months after the procedure. Approximately 8%–10% of all shunts placed become infected, resulting in shunt removal, replacement and significant morbidity and mortality.4 Previous studies have identified risk factors for shunt infection, such as previous shunt revisions, first shunt placement under 1 year of age, hydrocephalus resulting from hemorrhage and ventriculoatrial or complex initial shunt.1,4,5 Infection rates after shunt revision surgery are approximately 3-fold higher after the first revision and become even more frequent with each additional surgery.1,3–5
P. acnes is a Gram-positive pleomorphic diphtheroid-like anaerobic bacillus, and it is part of the normal skin flora.2,5 As identified previously, shunt infection with P. acnes frequently results in a mild clinical picture, can be associated with an abdominal pseudocyst and infections occur in the older child and adolescent.4
Diagnosis of CSF shunt infection is usually based on conventional microbiologic cultures. However, P. acnes can be difficult to isolate because of its slow growth and anaerobic requirements.2 When suspected, the laboratory should be alerted to extend incubation time and use appropriate media for cultures. However, in this case, the culture was not extended, and identification was only possible by broad-range 16S rRNA gene PCR. Though it may be difficult to differentiate colonization from infection, and false positive results may arise from this assay, we assumed it was a true pathogen because of suggestive clinical picture, CSF pleocytosis, the negative bacterial cultures, the absence of amplification of another possible contaminating organism (namely coagulase-negative staphylococci) and achievement of cure only after removal of the shunt. Molecular diagnostic techniques such as PCR are currently a powerful and important diagnostic tool, especially in cases of high clinical suspicion with negative CSF cultures.4,6,7 The broad-range 16S rRNA gene PCR identifies the 16S portion of rRNA that is present in almost all bacteria; DNA is extracted and amplified, and then the sequences obtained are compared with databases and the species identified.8,9
Despite being an agent of low virulence, eradication of P. acnes infections is difficult as P. acnes adhere to the inner surfaces of the shunt catheters and develop a biofilm. In these cases, total shunt removal is mandatory.6,7,10 Rifampin plays an important role in penetrating the biofilm but does not exclude the need for shunt replacement. Antibiotic-impregnated devices may be a good option in treating hydrocephalus after CNS shunt infection.3,11,12 Currently, the management of CNS shunt infection includes exteriorization of the distal catheter, parenteral antibiotics and shunt replacement once the CFS is sterile.
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