Acute disseminated encephalomyelitis (ADEM) is characterized by a brief but widespread attack of inflammation in the brain and spinal cord that damages myelin – the protective covering of nerve fibers. ADEM often follows viral or bacterial infections, or less often, vaccination for measles, mumps, or rubella. It bears a striking clinical and pathological resemblance to multiple sclerosis (MS).
The diagnosis if ADEM needs to be considered whenever there is a close relationship between an infection and the development of more than one neurological symptom, which are often accompanied by headache, fever, and an altered mental state. The symptoms tend to worsen over a few days, making it clear that the problem is a serious one.
Magnetic resonance imaging (MRI) scanning is an important part of the diagnosis. In ADEM, there are usually widespread, multiple changes deep in the brain in areas known as the white matter. The white matter is the part of the brain and spinal cord that contains the nerve fibers.
These nerve fibers are often covered by the protective coating called myelin, which looks white compared with the grey matter, which contains the nerve cells. There are also sometimes lesions in the grey matter deep in the brain as well. Often the areas affected can be more than half of the total volume of the white matter.
While these changes are characteristic, they are not specific for ADEM. The health care professionals in these cases must consider other diagnoses, such as multiple sclerosis (MS), direct brain infections, and sometimes tumors.
Over months these changes on MRI should gradually improve and even completely disappear.
Spinal Fluid Testing
A lumbar puncture is typically needed in patients with ADEM. This is partially to rule out direct infections or other processes that can look like ADEM. The lumbar puncture allows the neurological team to test the cerebrospinal fluid for many different things that assist in the diagnostic process.
The cerebrospinal fluid (CSF) or spinal fluid is a clear, colorless fluid that circulates in around the brain and spinal cord. It cushions the brain from hitting the inside of the skull, and may be important in removing chemicals from the brain.
In ADEM, the spinal fluid often shows an increase in white cells, usually lymphocytes. These cells are an active part of the immune system. Occasionally doctors can culture or measure a reaction to a specific virus or bacteria in the spinal fluid that may have triggered ADEM. In ADEM, there are often no oligoclonal bands. Oligoclonal bands are abnormal bands of proteins seen in certain spinal fluid tests that indicate activity of the immune system in and around the spinal fluid pathways. These bands are commonly found in multiple sclerosis. This difference may help to distinguish ADEM from MS.
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