Think outside the box: Acanthamoeba encephalitis following autologous haematopoietic stem cell transplantation.

Abstract

A 62-year-old female presented with a 5-day history of fever, headache, generalized weakness and altered mental status on day 17 after autologous haematopoietic stem cell transplantation. Physical examination was remarkable for repeated myoclonic jerks of the left wrist. Magnetic resonance imaging (MRI) of the brain revealed multiple hyper-intense ill-defined lesions, the largest one (4·5 cm diameter) in the right frontal lobe (top left). A lumbar puncture showed neutrophilic pleocytosis with elevated protein but was otherwise unremarkable. Despite initiation of corticosteroids and broad-spectrum antimicrobials (vancomycin, meropenem and amphotericin-B), the patient remained febrile. To determine the aetiology of her fevers and neurological abnormalities she underwent right frontal lobe needle biopsy. The next day she had raised intracranial pressure with signs of temporal lobe herniation and she expired shortly thereafter. The brain biopsy specimen showed necrotizing encephalitis, most consistent with granulomatous amoebic encephalitis (bottom left) with Acanthamoeba species being identified by indirect immunofluorescence (top right) and real time polymerase chain reaction (PCR). The patient's cerebrospinal fluid-derived DNA gave a threshold cycle (Ct) of 27·08 with the Acanthamoeba (Ac) primers and probe, and no Ct values were detected with either Naegleria fowleri (Nf) or Balamuthia mandrillaris (Bm) primers and probes (bottom right). Though rare, it is important to consider granulomatous amoebic encephalitis in the differential diagnosis of meningitis when bacterial, fungal and viral causes are excluded, especially in an immunocompromised host.