Acute Disseminated Encephalomyelitis (ADEM) in Children
What is ADEM?
Acute disseminated encephalomyelitis is an immune mediated inflammatory disorder of the CNS which predominantly affects the white matter of the brain, spinal cord and optic nerves. It is usually precipitated by an infection or vaccination.
Epidemiology of ADEM
ADEM can occur at any age, but it is more common in children than in adults. The mean age at presentation is from 5 to 8 years. Although there appears to be no gender predominance, two pediatric cohorts have reported a male predominance with female to male ratios of 0.6 and 0.8. The mean incidence of ADEM is 0.4/100,000/ year in the pediatric age group. A seasonal distribution in the winter and spring has been found in studies. A plethora of viral and bacterial pathogens and a number of vaccinations have been associated with ADEM.
Clinical presentation of ADEM
ADEM is usually a monophasic disorder. Neurological signs and symptoms appear days to weeks after an infections or vaccination with an average latency of 4 to 13 days. Prodromal symptoms often include constitutional, systemic and poorly localized neurological symptoms such as fever, headache, vomiting, lethargy and irritability. The initial neurologic symptoms are generally multifocal and determined by the location of the lesions within the CNS. These most commonly include altered level of consciousness (encephalopathy), pyramidal tract dysfunction including monoparesis, hemiparesis, ataxia and brainstem dysfunction including cranial nerve palsies and optic neuritis. Other clinical features include seizures and meningeal signs.
Diagnosis of ADEM
Diagnosis of ADEM is based on the clinical presentation, investigations including CSF studies and MRI findings. CSF may show lymphocytic pleocytosis with elevated protein levels. MRI brain shows multifocal, poorly marginated cerebral white matter lesions on T2- and FLAIR sequences that enhance with gadolinium. The lesions are usually large, asymmetric and can involve the subcortical and central white matter and cortical gray-white junction of the cerebral hemispheres, cerebellum, brainstem and spinal cord.
Treatment of ADEM
There is no standard therapy for ADEM. Current treatment approach is based on non-specific immunosuppression with intravenous steroids followed by oral prednisone taper. Other immunomodulatory therapies including IVIG or plasmapheresis are used in cases refractory to steroids. Supportive therapy and symptomatic treatment of associated symptoms such as seizures is important.
Research in ADEM
ADEM often poses a diagnostic and prognostic challenge for neurologists. One of the most pressing questions of a child presenting with ADEM is the future risk for conversion to MS. Identification of a biomarker that will help predict the development of MS after an ADEM event is critical. There is ongoing research to understand the worldwide epidemiology and distribution of ADEM. These studies will help to gain insight into the pathogenesis of ADEM and potential preventative measures.