Disseminated Encephalomyelitis
ADEM--An Acute Condition that Mimics Multiple Sclerosis (MS)
Nov 3, 2007
Acute disseminated encephalomyelitis (ADEM) is an inflammatory disorder very similar to multiple sclerosis (MS). Both disorders cause deterioration of the myelin sheath surrounding nerve fibers in the brain and spinal cord. Because acute disseminated encephalomyelitis usually occurs in children it is often confused with pediatric multiple sclerosis. Some researchers think that acute disseminated encephalomyelitis is a variant of multiple sclerosis that permanently resolves after one episode of illness.
Who is Affected?
People of any age can develop acute disseminated encephalomyelitis although it is most likely to occur in children. About 80 percent of all cases occur in children younger than age 10 years. and about 3 percent of all cases are reported in adults. ADEM is known to arise after viral infections, particularly measles, and after vaccinations, particularly those for rabies, pertussis, and influenza. Among adolescents, ADEM is three times more common than MS. Males are affected slightly more often than females.
Symptoms
Symptoms in acute disseminated encephalomyelitis come on suddenly and cause symptoms resembling encephalitis such as fever, fatigue, headache, gait disturbances, nystagmus, cranial nerve palsies, visual field deficits, irritability, changes in mental status, nausea, vomiting, and in severe cases seizures and coma. Visual loss can also occur if inflammation of the optic nerve develops. Fever is common in ADEM but not a typical symptom in MS. A particularly severe form of ADEM which causes hemorrhage is called acute hemorrhagic leukoencephalopathy (AHLE).
Signs
Both MS and ADEM cause perivenular round cell inflammation with patchy demyelination of nerve fibers. The inflammatory exudates in these disorders contains predominantly microglial cells. In both conditions there is evidence of T helper cells being sensitized to myelin proteins. Abnormalities in cytokine levels are similar in both disorders. The platelet count may be elevated in children with ADEM.
Disease Course
ADEM is characterized by one or sometimes two episodes of symptoms that resolve. Usually, symptoms of ADEM persist for several weeks and then resolve although in about one third of all cases, symptoms can persist for up to one year. MS is characterized by a relapsing remitting condition of multiple disease flares. Children who develop ADEM before age 10 are known to very rarely develop multiple sclerosis in later life. However, there are no tests to tell if someone with ADEM will go on to develop MS.
Diagnosis
Like MS, ADEM damages the white matter of the brain, and this can be seen on MRI. However, while ADEM shows new lesions, patients with MS will show old lesions because lesions develop in multiple sclerosis before symptoms occur. The lesions in ADEM may also show signs of hemorrhage. This does not occur in multiple sclerosis. By correlating the clinical history including previous viral illnesses and recent vaccines along with findings from imaging tests doctors can often differentiate MS from acute disseminated encephalomyelitis. However, the disorders may overlap and imaging tests alone should not be relied on.
An electroencephalogram (EEG) shows disturbances in the normal sleep rhythms in patients with ADEM. Focal or generalized slowing, the appearance of sharp waves, rhythmic delta, or spikes in the waking state are seen in the early stages of ADEM. The absence of these findings suggests MS.
Treatment
Corticosteroids are the primary therapy for ADEM. Anticonvulsants are used in patients who present with seizures. If corticosteroids are stopped too soon, a relapse or second bout of ADEM can occur.
Resources:
National Organization for Rare Disorders
National Institute of Neurological Disorders and Stroke
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