What is acute disseminated encephalomyelitis?
Acute disseminated encephalomyelitis (ADEM) is a rare neurological disorder. It affects children more than adults, but can affect anyone.
Symptoms and Causes
What are the causes and/or risk factors associated with acute disseminated encephalomyelitis?
We know that ADEM usually follows an infection of some kind. In 50 to 75 percent of cases, the beginning of the disease is preceded by a viral or bacterial infection, usually a sore throat or cough (upper respiratory tract infection). Many different bacteria, viruses and other infections have been related to ADEM, but the disease does not appear to be caused by any one infectious agent. Most cases of ADEM begin about 7 to 14 days after the infection.
ADEM appears to be an immune reaction to the infection. In this reaction, the immune system, instead of fighting off the infection, causes inflammation in the central nervous system. Inflammation is defined as the body's complex biological response to harmful stimuli, such as infectious agents, damaged cells, or irritants. Inflammation is a protective attempt to remove the injurious stimuli and initiate the healing process. In the case of ADEM, the immune response is also responsible for demyelination, a process in which the myelin that covers many nerve fibers is stripped off.
What are the symptoms of acute disseminated encephalomyelitis?
More than half of patients have an illness, usually an infection, two to four weeks before developing ADEM. Most of these illnesses are viral or bacterial, often no more than an upper respiratory tract infection. In children with ADEM, prolonged and severe headaches occur. In addition, the patient develops fevers during the ADEM course.
Along with this pattern, the patients usually get neurological symptoms which may include:
- Confusion, drowsiness, and even coma
- Unsteadiness and falling
- Visual blurring or double vision (occasionally)
- Trouble swallowing
- Weakness of the arms or legs
In adults with ADEM, motor (movement) and sensory (tingling, numbness) symptoms tend to be more common. Overall, what triggers a diagnosis of ADEM is a rapidly developing illness with neurological symptoms, often with fever and headache, usually following an upper respiratory tract infection, and which has significant MRI and spinal fluid findings consistent with ADEM.
Diagnosis and Tests
How is acute disseminated encephalomyelitis diagnosed? What tests might be used?
The diagnosis of 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 healthcare 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.
Management and Treatment
How is acute disseminated encephalomyelitis (ADEM) treated?
ADEM is a rare disease, and so there are no well-designed clinical trials comparing one treatment with placebo, or one treatment with another. Everything we know about treatment in ADEM comes from small published series of cases, and there are no guidelines for treatment of ADEM yet.
At this time, intravenous methyl-prednisolone (for instance, Solu-Medrol®) or other steroid medications are the front-line treatment for ADEM. Usually these medications are given over a five- to seven-day course, followed by a tapering dose of oral steroids. The aim is to reduce inflammation and speed recovery from the disease.
Patients on steroids need to be monitored for increased blood glucose, low potassium, and sleep disturbance. There may be mood changes (irritability, crying, anxiety) when people are on steroid therapy. Other short-term complications of steroid therapy include weight gain, flushed cheeks, facial swelling, and a metallic taste (when using IV Solu-Medrol®).
If a patient does not respond to IV methylprednisolone, the next line of treatment may be intravenous immune globulin (IVIG). This is an intravenous treatment using a blood product which has been shown to reduce the activity in certain immune diseases, including ADEM. Treatment is usually given for a few hours daily over five days for ADEM. IVIG has the same risks as any blood product (allergic reaction, infection); it also sometimes causes shortness of breath due to fluid overload. Rarely, patients lack an antibody important to the system and may react more strongly to IVIG.
Another approach to treatment is a process called plasmapheresis. This is a treatment in which the blood is circulated through a machine that withdraws components of the immune system from the circulation, reducing immune activity. It is usually a process which takes a few hours and is done every other day for 10 to 14 days, often as part of a hospital stay. It may require the placement of a central venous catheter to allow for blood to be removed from the system rapidly. Risks of plasmapheresis include discomfort from taking blood, sometimes a tendency to bleed due to a reduction in platelets, and infections.