What is neuromyelitis optica?
Neuromyelitis optica (NMO), also known as Devic’s disease, is a rare
inflammatory and demyelinating disorder of the central nervous system (CNS)
that primarily affects the spinal cord and optic nerves. It was first described
by Eugène Devic in 1894. NMO is an autoimmune condition in which the immune
system mistakenly attacks healthy tissue, specifically targeting the myelin
sheath, the protective covering of the optic nerve and spinal cord. in 1894.
Types of Neuromyelitis Optica
There are two main types of NMO:
1. Relapsing Neuromyelitis Optica:
- This form is characterized by an initial attack of
optic neuritis and transverse myelitis, followed by multiple relapses
over several years.
- Each attack can cause cumulative damage, sometimes
leading to permanent disability due to damage to the optic nerve and/or
spinal cord.
- This type affects females more frequently than males,
with a ratio greater than 4:1.
2. Monophasic Neuromyelitis Optica:
- In this form, patients experience one or more attacks
over a short period (days or weeks) without future relapses.
- This type affects both sexes equally.
Who is affected?
NMO can develop at any age, with two peak onset periods: one in childhood
and another in adults in their 40s. Women are more commonly affected than men,
with a ratio of over 4:1.
Symptoms of NMO?\
The most common symptoms of NMO include:
1. Optic neuritis:
- Inflammation and demyelination of the optic
nerve, leading to vision impairment, eye pain, and sometimes complete vision
loss in one or both eyes. movement pain.
2. Transverse Myelitis:
- Inflammation of the spinal cord, causing weakness,
numbness, and sensory disturbances in the limbs.
- Possible bladder and bowel dysfunction.
- The severity of symptoms depends on the extent and
location of spinal cord inflammation.he spinal cord.
Diagnosing NMO
Diagnosis of Optic Neuritis:
- A comprehensive medical evaluation, including blood tests, to rule
out related conditions.
- Colour vision tests, such as the Ishihara colour chart and
Farnsworth-Munsell hue tests, to assess colour blindness.
- Visual evoked potentials (VEP) to measure the speed of nerve signal
transmission.
Diagnosis of Transverse Myelitis:
- Magnetic Resonance Imaging (MRI): Used to
identify spinal cord lesions affecting three or more segments.
- Lumbar Puncture (Spinal Tap): A sample of
cerebrospinal fluid is tested for elevated white blood cell levels and the
presence of specific proteins associated with NMO.
- NMO-IgG Antibody Test: The presence of NMO-IgG
(anti-Aquaporin-4 antibody) supports the diagnosis but is not mandatory.
Causes of NMO
NMO is an autoimmune disorder where the immune system mistakenly attacks
healthy tissue. Researchers believe that NMO-IgG, an antibody found in over
two-thirds of NMO patients, damages Aquaporin-4, a protein that regulates water
balance in CNS cells. The exact cause of NMO remains unknown, but it may be
triggered by infections or other environmental factors in genetically
predisposed individuals.
Treatment for NMO
Although there is no cure for NMO, treatments focus on managing symptoms,
stopping attacks, and preventing relapses.
Acute Treatment:
- High-dose corticosteroids (e.g., methylprednisolone)
are used to reduce inflammation during an attack.
- Plasma exchange (plasmapheresis) may be used for
severe cases that do not respond to steroids.
Long-Term Treatment:
- Immunosuppressive drugs (e.g., rituximab,
azathioprine, mycophenolate mofetil) help prevent future attacks.
- Some patients may require long-term low-dose steroids
if relapses occur frequently.
Symptom Management:
- Neuropathic pain, muscle spasms, stiffness, and
bladder/bowel issues can be managed with medications and physical
therapy.
What is the prognosis for individuals with NMO?
The course of NMO is unpredictable. Many individuals experience relapses
that progressively damage the nervous system, leading to cumulative disability.
Permanent limb weakness is common, and in severe cases, patients may lose
vision in both eyes and mobility in their arms and legs. Respiratory failure
due to spinal cord damage can be life-threatening.
Early diagnosis and treatment are crucial in preventing severe disability
and improving the quality of life for those with NMO.