Filamentous rods in the cerebrospinal fluid of a child with ventriculoperitoneal shunt: “Separation Anxiety” at the microscopic level!

Abstract

Clinical Vignette introduCtionThe morphologic recognition of organisms remains an important component of the diagnostic work up of a specimen in general pathology practice. An accurate interpretation requires familiarity with an organism's typical morphology as well as morphologic variations, including artificial changes. This case report illustrates the morphologic transformation of antibiotic altered Pseudomonas aeruginosa in the cerebrospinal fluid of a young boy. CliniCal historyOur patient is a 17-year-old boy with a history of hydrocephalus and placement of a ventriculoperitoneal shunt who presented with fever. Recent medical history included bacteremia, with blood cultures positive for Propionibacterium acnes. On hospital day 1, the patient was started on empiric broad-spectrum antibiotics: vancomycin (20 mg/kg every 6 h); cefepime (intravenous, 50 mg/kg every 8 h); Flagyl (intravenous, 10 mg/kg every 8 h); and amikacin (intravenous, 20 mg/kg daily). Cultures from cerebrospinal fluid (CSF) grew pansensitive P. aeruginosa. Subsequent peritoneal fluid and distal catheter cultures on day 2 postadmission grew P. aeruginosa, and subsequently, the shunt was removed on day 3 postadmission (shunt hardware cultures also grew P. aeruginosa). Vancomycin and amikacin were subsequently discontinued (3 days of therapy each). On day 7 postadmission, a repeat CSF fluid analysis showed an elevated white blood cell (WBC) count of 674, and gentamicin (intravenous, 2.5 mg/kg every 8 h) was added for secondary Gram-negative coverage. Flagyl was discontinued on postadmission day 9 after anaerobic cultures remained negative (9 days of therapy), and gentamicin was discontinued on postadmission day 10 given recent negative routine CSF cultures (4 days of therapy). Unfortunately, a culture from the patient's external ventricular drain on postadmission day 11 was again positive for P. aeruginosa, and ciprofloxacin (intravenous, 10 mg/kg) was added on postadmission day 12. Subsequent cultures were negative, Certain bacteria and antibiotic combinations can result in unusual morphologic transformations such as the creation of septate filamentous bacterial rods, where division is preserved, but separation is inhibited. This is often seen when subinhibitory concentrations of antibiotics are administered. Herein, we describe this phenomenon in the case of a teenage boy with an infected ventriculoperitoneal shunt, whose culture-proven Pseudomonas aeruginosa took on a filamentous appearance following antibiotic treatment. This transformation is important to recognize, so it is not misconstrued as fungal hyphae, committing the patient to unnecessary treatment.