Acute Disseminated Encephalomyelitis
Background
Acute disseminated encephalomyelitis (ADEM) is an inflammatory disorder affecting the brain (enceph-) and/or spinal cord (myelitis). It is a rare condition mostly affecting children and is usually monophasic meaning it only occurs once. It is usually preceded by an infection, even a trivial one, and occasionally by immunisation.
Credits
Medical text written by October 2010 by Leena D Mewasingh. Last updated June 2018 by Leena D Mewasingh, Consultant Paediatric Neurologist and Honorary Senior Clinical Lecturer, St Mary’s Hospital, Imperial College Healthcare NHS Trust, London, UK.
Although great care has been taken in the compilation and preparation of all entries to ensure accuracy, we cannot accept responsibility for any errors or omissions. Any medical information is provided is for education/information purposes and is not designed to replace medical advice by a qualified medical professional.
There is often an infection that occurs before the diagnosis of ADEM, or even an immunisation, the interval varying between several days up to one month, the average being one to two weeks. In a minority of cases there is no clear preceding illness. At the beginning, symptoms can be non-specific but nonetheless worrying, such as fever, headache, stiff neck, a loss of appetite and vomiting. This is usually followed by or accompanied with a decreased conscious level such that the child may seem confused, lethargic or drowsy and does not respond in their normal way. For a diagnosis of ADEM to be made, a child’s level of consciousness must be affected and this is referred to as ‘acute encephalopathy’. At times the child can even slip into coma.
Other symptoms include:
- difficulties standing or walking
- hemiparesis (weakness down one side of the body)
- balance problems or ataxia (unsteadiness)
- cranial nerve palsies (paralysis of the nerves that emerge directly from the brain)
- visual impairment or visual loss due to inflammation of the optic nerve (eg optic neuritis) often involving both eyes
- epileptic seizures (these are more common in the younger child – five years old or younger).
Why ADEM occurs remains poorly understood. The risk of developing ADEM seems to be dependent on an interaction between different factors: an individual’s genetic predisposition, exposure to infectious agents or to immunisation and the individual’s immune response to the latter.
As ADEM is generally preceded by an infection, this suggests an immune/inflammatory process is important. Whilst many different bacteria, viruses and other infections have been related to ADEM, this condition does not appear to be caused by any one specific infectious agent.
A special committee, the International Pediatric Multiple Sclerosis Study Group (IPMSSG*) was brought together to define ADEM, given variations in its definition until then, and also because there are no diagnostic tests for this condition. The group established criteria for the definition of ADEM in 2007, which were recently reviewed and amended in 2013 and are now largely accepted as a definition to aid a working diagnosis of ADEM.
In the early stages of the illness, a child may be thought to have meningitis or encephalitis. The diagnosis of ADEM is made based upon i) the clinical history and its evolution, ii) brain imaging and iii) other tests.
Magnetic resonance imaging (MRI) scans of the head are done and often show changes as described by the IPMSSG* criteria. Other tests include a lumbar puncture, where a small amount of fluid called cerebrospinal fluid (CSF) is removed from the spine with a needle inserted in the lower back. This fluid is analysed and in ADEM it is often abnormal with an increase in white cells and protein. An electroencephalogram (EEG), which records the surface brain activity, is also done and often found to be abnormal.
In the initial stages, antibiotics and antiviral drugs are given in the veins (intravenously). When ADEM is diagnosed, high-dose steroid (methylprednisolone) given intravenously (through a vein) for a few days is the main form of treatment. Most children recover significantly, if not completely, and overall the prognosis is very good.
Other treatments used are: intravenous immunoglobulin (IVIG). Throughout the illness the child has to be monitored closely. At times this can mean intensive care with the child placed on a ventilator, especially if the child’s breathing or swallowing is affected.
Steroids and IVIG are treatments that can change the body’s immune response, which is known as immunomodulation. There is often a dramatic improvement after this type of treatment.
Some research studies of children that had ADEM have reported a small group of patients who then went on to develop multiple sclerosis. There is a lot of research that is ongoing in this area.
Inheritance patterns
It is thought that an individual’s genetic make-up can make some people more likely to develop ADEM in the context of some infectious triggers, this is known as ‘genetic susceptibility’. However this is difficult to prove. ADEM is not thought to be a ‘genetic or inherited’ condition as such.
Prenatal diagnosis
Not applicable.
Information and support in the UK for acute disseminated encephalomyelitis is provided by the Encephalitis Society (see entry Encephalitis).