Neuromyelitis optica (NMO), also known as Devic's disease, is an autoimmune disorder that affects the central nervous system, primarily the optic nerves and spinal cord. It is distinct from multiple sclerosis (MS) and requires different management and treatment approaches. However, in its early stages, NMO may present with symptoms that overlap with MS, leading to potential misdiagnosis or delayed diagnosis. Some signs of NMO that may be overlooked by doctors during the initial evaluation for MS include:
Selective Involvement of Optic Nerves and Spinal Cord: In NMO, optic neuritis (inflammation of the optic nerves) and transverse myelitis (inflammation of the spinal cord) are prominent features. These two areas are typically affected simultaneously or in a relapsing manner. In contrast, MS often involves multiple regions of the central nervous system, and optic neuritis and myelitis are less common as initial symptoms.
Severe and Rapid Vision Loss: NMO-related optic neuritis tends to cause more severe and rapid vision loss compared to typical MS-related optic neuritis. This rapid progression of visual impairment may be an indicator of NMO rather than MS.
Longer Spinal Cord Lesions: MRI findings in NMO often show longitudinally extensive transverse myelitis (LETM), which means the spinal cord lesion extends over three or more vertebral segments. In MS, spinal cord lesions are usually shorter.
Lesion Location and Enhancement Pattern: In NMO, spinal cord lesions tend to affect the central portion of the cord, while in MS, they are more often seen around the periphery. Additionally, NMO lesions may show different enhancement patterns on MRI compared to MS lesions.
Bilateral Optic Neuritis: While bilateral optic neuritis can occur in MS, it is more characteristic of NMO. Simultaneous inflammation of both optic nerves may suggest NMO over MS.
Absence of Typical MS Features: NMO lacks some of the hallmark features of MS, such as brain lesions in specific areas like periventricular, corpus callosum, and juxtacortical regions, and the presence of oligoclonal bands in the cerebrospinal fluid (CSF).
Association with Aquaporin-4 Antibodies: The majority of NMO patients have antibodies against a protein called aquaporin-4 (AQP4), which are not typically found in MS. Testing for these antibodies can aid in distinguishing NMO from MS.
It is essential for doctors to be aware of the distinguishing features between NMO and MS to ensure accurate and timely diagnosis. If there is suspicion of NMO based on clinical presentation and imaging findings, additional tests, such as AQP4 antibody testing, should be considered to confirm the diagnosis. Early and accurate diagnosis is crucial for implementing appropriate treatment and preventing potential complications associated with NMO.