Acute disseminated encephalomyelitis (ADEM) is a neurological, immune-mediated disorder in which widespread inflammation of the brain and spinal cord damages tissue known as white matter. White matter is tissue composed of nerve fibres, many of which are covered by a collection of fats and proteins known as myelin. Myelin, which collectively may be referred to as the myelin sheath, protects the nerve fibres, acts as an insulator and increases the speed of transmission of nerve signals. Damage to the myelin sheath affects the nerve’s ability to transmit information and potentially can cause a wide range of neurological symptoms.
Causes of Acute disseminated encephalomyelitis (ADEM)
The exact cause of ADEM is not known. However, most clinical investigators agree that the disorder is most likely the result of an abnormal immune system response to an infection or other trigger. Many researchers suggest that ADEM may represent an abnormal immune reaction directed against the body’s own tissues (autoimmune disorder). In autoimmune disorders, the body’s natural defences (e.g., antibodies, lymphocytes) against substances that are perceived as foreign (antigens) inappropriately begin to attack healthy tissues, for unknown reasons.
In some cases, a viral infection precedes the development of symptoms by two days to four weeks. Less often, the disorder may follow a vaccination. However, a preceding event is not always identified and some cases appear to occur spontaneously. Typically, ADEM is considered a monophasic disorder, which is a disorder that has a single occurrence or one phase in a particular individual.
The progression and severity of ADEM varies from one person to another. Initial symptoms usually develop rapidly and may include various symptoms common to many different illnesses (nonspecific symptoms) including fever, headaches, irritability, fatigue, lethargy, a general feeling of ill health (malaise), unintended weight loss and abdominal complaints including nausea and vomiting. In some cases, these symptoms may be followed by mental status changes such as confusion, stupor, delirium and, potentially, coma.
The symptoms of ADEM may also be affected by age of onset. Seizures are common in children and adults. Long-lasting fevers and headaches are more common in children than adults. Sensory deficits predominantly affect adults.
Diagnosis of Acute disseminated encephalomyelitis (ADEM)
A diagnosis of ADEM is made based upon identification of characteristic symptoms, a detailed patient history, a thorough clinical evaluation and a variety of specialized tests including imaging techniques such as magnetic resonance imaging (MRI). An MRI uses a magnetic field and radio waves to produce cross-sectional images of particular organs and bodily tissues and can demonstrate characteristic brain lesions in individuals with ADEM. Additional tests to exclude other conditions may also be performed. Such tests may include infectious, immunologic, and metabolic tests.
No standard therapy for ADEM has been established. Most therapies that have been used to treat ADEM have some effect of suppressing the activity of the immune system (immunosuppressive therapy). Such therapies include corticosteroids, immunoglobulin (IVIg) therapy, or plasmapheresis.
High dose regimens of corticosteroids have commonly been used to treat individuals with ADEM and generally are considered the mainstay of treatment. Corticosteroids have led to an improvement of symptoms in many cases. Corticosteroids are the most widely reported therapy for individuals with ADEM. Methyl prednisone is a specific corticosteroid that is commonly used for ADEM.