What Is Acute Disseminated Encephalomyelitis?
The central nervous system is a complex organ system vital for the functioning of the entire body. It is the key regulating center that influences other organ systems. Hence the brain and spinal cord, important constituents of the central nervous system, are well shielded from external and internal detriments. Meninges are the protective membranes covering the brain and spinal cord, thus efficiently safeguarding these vital organs. The nerve fibers are also encased within a protective case known as the myelin sheath. However, infections and inflammation due to various conditions may affect the central nervous system. Acute disseminated encephalomyelitis (ADEM) is a rare, inflammatory, neurological condition that damages the protective myelin sheath. Acute disseminated encephalomyelitis (ADEM) is considered an autoimmune disease that causes inflammation of the brain and spinal cord and, occasionally, the optic nerves. It affects children mostly. The prognosis is generally good, without any neurological deficits.
What Is the Cause of Acute Disseminated Encephalomyelitis?
Acute disseminated encephalomyelitis is considered a post-infection complication as most cases are preceded by a viral or bacterial infection, usually an upper respiratory tract infection. Though the exact etiopathogenesis is unknown, studies have linked it to an autoimmune response, which is presumed to be an immune response to the infection. Instead of warding off the pathogens, the immune system attacks the cells and tissues of the central nervous system, thus resulting in inflammation and demyelination (damaging the myelin sheath).
Though there is no direct evidence, acute disseminated encephalomyelitis (ADEM) has also been reported after certain vaccinations, such as measles or rabies. A minority of cases have also been reported to occur sporadically.
The risk factors include:
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Age: Children are mostly affected.
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Sex: This condition is more prevalent in boys.
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Climate: Mostly seen during winter and springtime.
What Are the Signs and Symptoms of Acute Disseminated Encephalomyelitis?
The symptoms may be of sudden onset and may also progress rapidly. They include:
Symptoms in children:
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High fever.
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Fatigue and malaise.
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Body pain.
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Vomiting.
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Sleepiness.
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Confusion and irritability.
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Blurred vision.
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Slurred speech.
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Difficulty maintaining balance.
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Severe cases may result in hemiparesis, seizures, and coma.
Symptoms in Adults:
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Peripheral neuropathy.
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Numbness or tingling sensation in the extremities.
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Behavioral changes and depression.
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Amnesia.
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Involuntary movements.
Few publications have reported acute disseminated encephalomyelitis following Covid-19 infection. These cases were promptly diagnosed and treated to prevent poor prognosis. A severe hyperacute, fulminant variant of acute disseminated encephalomyelitis (ADEM) is acute hemorrhagic leukoencephalitis (AHLE). Similar to acute hemorrhagic leukoencephalitis (ADEM), acute hemorrhagic leukoencephalitis (AHLE) also follows a viral or bacterial infection; however, it is more severe and is associated with a poor prognosis. Survivors often tend to have neurological deficits.
How Is Acute Disseminated Encephalomyelitis Diagnosed?
The diagnosis of acute disseminated encephalomyelitis is challenging. However, this condition should be contemplated whenever a neurological symptom develops post an infectious period. The diagnostic workup is as given below:
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Physical Signs and Symptoms: The physical signs and symptoms may not be conclusive but indicate a neurological disorder that may require further diagnostic testing.
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Blood Analysis: The blood picture shows lymphocytic pleocytosis with an increase in the protein count. The erythrocyte sedimentation rate (ESR), however, remains normal.
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Cerebrospinal (CSF) Analysis: A lumbar puncture may be performed to assess the spinal fluid. The cerebrospinal fluid primarily protects the brain. The spinal fluid analysis shows mononuclear cerebrospinal fluid (CSF) cellularity, usually the lymphocytes.
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Radiological Imaging: Magnetic resonance imaging (MRI) is an important radiologic diagnostic tool to arrive at a confirmatory diagnosis and rule out other conditions. It can also help ascertain the course of the diseases and the outcome. MRI reveals hyperintense lesions of the white matter (primary areas of the brain containing the nerve fibers).
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Brain Biopsy: A histopathological examination of a biopsied tissue from the brain may reveal perivascular demyelination with lymphocytic infiltration. A brain biopsy is rarely advocated in acute disseminated encephalomyelitis (ADEM).
What are the differential diagnoses?
Acute disseminated encephalomyelitis (ADEM) has features overlapping two similar neurological conditions: acute hemorrhagic leukoencephalitis (AHLE) and multiple sclerosis. The differences are described below:
Acute Hemorrhagic Leukoencephalitis: A rare inflammatory condition affecting the brain and spinal cord.
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Most commonly seen in adults.
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Hyperacute onset.
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Predominant leukocytosis.
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Granulocytic pleocytosis.
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Raised erythrocyte sedimentation rate (ESR).
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The prognosis is poor with a high mortality rate.
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Coma and death are common.
Multiple Sclerosis: A disease in which the immune system destroys the protective covering of nerves.
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Most common in adults.
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Fever, headache, seizures, and confusion symptoms are rarely seen.
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Does not follows a viral or bacterial illness.
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Repeated episodes over a period.
How Is Acute Disseminated Encephalomyelitis Treated?
Acute disseminated encephalomyelitis (ADEM) is a rare disease; hence, there are no defined diagnostic or therapeutic criteria. The first line of treatment involves intravenous steroids to reduce inflammation. Intravenous immunoglobulin and plasmapheresis may be considered if the patient is not responding to corticosteroids. Severe cases may require Cyclophosphamide or Mitoxantrone (chemotherapeutic drugs). Supportive physical therapy, occupational therapy, or speech therapy may be required. Follow-up MRI may be needed to ensure the inflammation has subsided and there is no new scar formation.
How Is the Prognosis?
Though recovery is slow, children tend to recover completely within four to six weeks. The prognosis is extremely good as there are no neurological deficits post-recovery. Complete remission is seen in 60 to 80 percent of children; however, some might have lasting muscle weakness or vision problems. The mortality rate is extremely low, about one to three percent. Studies have reported a single episode of this disease, but it can rarely recur within a few months, especially with an abridged treatment.
Conclusion
Acute disseminated encephalomyelitis (ADEM) is a rare neurological condition that can affect anyone but is seen more in children. An episode of infectious illness usually precedes it. The symptoms though manageable, require immediate medical attention to rule out other neurological disorders. The prognosis is favorable with complete recovery. However, extensive studies are required to define certain diagnostic and therapeutic criteria to identify this condition and its lesser-known variant acute hemorrhagic leukoencephalitis (AHLE).
