Paediatric opioid use‐associated neurotoxicity with cerebellar oedema (POUNCE) syndrome is a toxic encephalopathy in children with opioid overdose that features prominent cerebellar oedema. Cerebellar predominance, along with variable supratentorial involvement, appears to be a distinct pattern of opioid neurotoxicity in children ^1,2.

Terminology

POUNCE is likely part of a pathophysiologic spectrum that also includes cerebellar, hippocampal, and basal nuclei transient oedema with restricted diffusion (CHANTER) syndrome (occurring in adults) and the milder opioid-associated amnestic syndrome (also in adults, but involves the hippocampi alone).

It may also share some similarities with chasing the dragon leukoencephalopathy (which occurs specifically after heroin vapour inhalation), although this relationship is less established.

Epidemiology

POUNCE is rare but increasing, particularly in the USA, due to the current opioid epidemic ⁸. It affects children exposed to opioids either accidentally (younger children) or recreational use/abuse (adolescents) ¹.

Clinical presentation

POUNCE syndrome presents with respiratory depression and decreased level of consciousness ¹. Other common clinical findings include mutism and ataxia ¹.

Radiographic features

Imaging shows bilateral cerebellar oedema and a variable degree/distribution of supratentorial white matter lesions (hyperintense on T2-weighted MRI, hypodense on CT) ^1-7. Diffusion restriction has been reported in some cases ^2,5-7.

Mass effect can result in hydrocephalus and tonsillar herniation.

Treatment and prognosis

In addition to cessation of opioid use and general supportive care (e.g. respiratory support if needed), treatment focuses on management of hydrocephalus (e.g. EVD placement) and posterior mass effect (e.g. posterior fossa decompression) ⁶.

Due to the small number of reported patients, generalisations regarding prognosis are unavailable; however, with prompt and appropriate management, many patients make excellent recovery ⁶.

Differential diagnosis

• acute cerebellitis

• hypoxic-ischaemic encephalopathy

• CHANTER syndrome

  • probably the same condition but in adults