Acute necrotizing encephalopathy

Acute necrotising encephalitisencephalopathy, also referred as acute necrotising encephalopathy of childhood (ANEC) is, is a rare type of encephalopathy characterised by multiple bilateral brain lesions, mainly involving the thalami, but also the putamina, internal and external capsules, cerebellar white matter, and the brainstem tegmentum.

Epidemiology

Acute necrotising encephalitis of childhood is a rare condition with less than 150 cases reported in the literature. From the first case described in 1995, many cases have been reported in Asia as well as many Western countries. Most cases are sporadic; however, a few cases of recurrent and/or familial episodes have been reported suggesting an inherited pattern.

Although the initial publications were in the paediatric population, multiple further reports showed the condition to also occur in adulthood⁸.

Clinical features

Acute necrotising encephalitis of childhood is seen around the age of 4 years. Clinically, it is characterized by acute encephalopathy, with dramatic neurological deficits/symptoms. A viral etiology has been proposed in some cases; viral prodrome hence may precede the neurological deficits.

Pathology

The aetiology and the pathogenesis of acute necrotising encephalitis of childhood isare only partially clear. Usually, it develops secondary to viral infections, including influenza A and influenza B, parainfluenza, varicella, and enterovirus.

Pathologically, the lesions show oedema, haemorrhage and necrosis. ANECAcute necrotising encephalopathy is characterised by the lack of inflammatory cells in affected brain parenchyma in comparison to the more common entities of acute disseminated encephalomyelitis and acute hemorrhagic encephalitis ¹.

Radiographic features

CT

On CT, the corresponding thalamic, putamina, cerebral, cerebellar and brainstem abnormalities are hypodense.

Intracranial hemorrhage and cavitation may also be seen, both of which are associated with a worse prognosis.

MRI

In most cases of acute necrotising encephalitis of childhood, there is bilateral symmetrical thalamic involvement. Abnormal signals on MRI are hypointense on T1 and hyperintense on T2. Restricted diffusion of the involved regions can be seen. ⁷ These findings can be quite extensive. Haemorrhage, cavitation, and post-contrast enhancement are also seen.

Treatment and prognosis

Acute necrotising encephalitis of childhood carries a very poor prognosis; the mortality rate is near 70%. Treatment is mainly supportive, as the precise etiology remains unknown.

Differential diagnosis

If characteristic symmetric imaging findings are present, the differential diagnosis is limited. Lactic acidosis is not a classic finding of ANEC. Otherwise, the differential diagnoses include:

• acute disseminated encephalomyelitis (ADEM)
• Leigh syndrome
  • associated with hypoglycemia, hyperammonemia and lactic acidosis
• Reye syndrome
  • associated with hypoglycemia, hyperammonemia and lactic acidosis

Clinically, acute necrotising encephalitis of childhood may be differentiated from ADEM by an early onset of encephalitic features just after the prodromal illness while in ADEM, they may take 1 to 2 weeks to develop.