Acanthamoeba rhombencephalomyelitis: Novel white matter tract-based neuroinvasive pattern in a retrospective observational study from India.

OBJECTIVE

To describe a distinct rhombencephalomyelitis pattern in patients with central nervous system infection due to free-living amoebae, differing from the classical granulomatous amoebic encephalitis phenotype.

METHODS

This retrospective observational study included twelve consecutive patients with brainstem and/or spinal cord involvement associated with central nervous system infection due to Acanthamoeba species at a tertiary care centre in Kerala, India. Diagnosis was confirmed by wet mount examination and amoeba species-specific 18S rRNA PCR of cerebrospinal fluid. Comprehensive evaluation excluded bacterial, mycobacterial, fungal, and autoimmune etiologies.

RESULTS

Twelve patients (seven men; median age 50 years; IQR: 33-60 years) presented with subacute cranial neuropathies (58.3%) and/or gait disturbance (91.7%). Seven (58.3%) were immunocompetent; only two had traditional risk factors (ritualistic nasal ablution). MR scan demonstrated involvement of the spinal cord (66.7%), pons (58.3%), middle cerebellar peduncle (50%), and medulla (41.7%). This distinctive neuroimaging pattern reflected white matter tract-based spread along cerebellar peduncles and/or corticospinal tracts. CSF analysis revealed lymphocytic pleocytosis (median: 12 cells/mm3, IQR: 5-47). with hypoglycorrhachia (CSF-to-blood glucose ratio 0.45 IQR: 0.4-0.5). Acanthamoeba spp. were confirmed by CSF PCR in ten (83.3%) and presumptively by wet mount examination in two (16.7%). Nine patients (75.0%) survived, of whom eight (66.7%) achieved favourable functional outcome (mRS 1-2).

CONCLUSION

Acanthamoeba spp. causes distinct white matter tract-based non-granulomatous rhombencephalomyelitis. Neurologists should screen for free-living amoebae CNS infection even without traditional risk factors, as this pattern may mimic demyelinating disorders (NMOSD, MOGAD, ADEM, or MS). When identified early, Acanthamoeba rhombencephalomyelitis carries a favourable prognosis.