Acute leukoencephalopathy with restricted diffusion (ALERD) in a toddler: A diagnostic challenge unmasking hereditary sensory autonomic neuropathy type 4.

A toddler boy presented with irritability, vomiting, fever and multiple episodes of seizures, followed by status epilepticus on day 4 of illness. The child had a history of reduced pain perception, recurrent unexplained febrile episodes, self-injurious behaviour and reduced sweating noted since birth. On examination, the Glasgow Coma Scale score was 6/15, with evidence of dental attrition, non-healing wounds, hypotonia, reduced power and sluggish reflexes. MRI brain revealed bilateral symmetrical diffusion restriction in the subcortical white matter, consistent with Acute Leukoencephalopathy with Restricted Diffusion (ALERD). The child received intravenous immunoglobulin and intravenous methylprednisolone for 5 days, and by the end of therapy showed about 60% improvement in encephalopathy. Exome sequencing revealed compound heterozygous variants, likely pathogenic in the NTRK1 gene. The child was diagnosed with ALERD in the context of hereditary sensory autonomic neuropathy (HSAN). This case illustrates HSAN type 4, which can present as ALERD, posing diagnostic challenges.