Abstract

A previously well 16-year-old boy developed a rapid-onset hypokinetic syndrome, coupled with a radiological appearance of extensive and highly symmetrical basal ganglia and white matter change. The diagnostic process was challenging and we systematically considered potential causes. After excluding common causes of this clinico-radiological picture, we considered common disorders with this unusual radiological picture and vice versa, before finally concluding that this was a rare presentation of a rare disease. We considered the broad categories of: metabolic; toxic; infective; inflammatory, postinfective and immune-mediated; neoplastic; paraneoplastic and heredodegenerative. Long-term follow-up gave insight into the nature of the insult, confirming the monophasic course. During recovery, and following presumed secondary aberrant reinnervation, his disorder evolved from predominantly hypokinetic to hyperkinetic. Here, we explore the process of finding a ‘best-fit’ diagnosis: in this case, acute necrotising encephalopathy.