HILTON HEAD—Multiple sclerosis (MS) is the most common demyelinating disease, and its mimics are rare, according to an overview provided at the 39th Annual Contemporary Clinical Neurology Symposium. Given that the treatments and outcomes for MS and its mimics are so different, neurologists should take care to establish a diagnosis early, said Sid Pawate, MD, Assistant Professor of Neurology at Vanderbilt University School of Medicine in Nashville.
Sid Pawate, MD
Because of the varied clinical presentation of MS, a wide variety of conditions enter the differential diagnosis. Because of the central role that MRI plays in MS diagnosis, imaging mimics that cause white matter lesions also need to be considered, said Dr. Pawate. Typically, the white matter lesions seen in MS are periventricular, juxtacortical, and callososeptal in location. Infratentorially, cerebellar peduncles are a common site. The lesions tend to be ovoid, are 3 mm to 5 mm or larger, and appear hyperintense on T2 and FLAIR sequences. Acute lesions may show restricted diffusion or enhancement after the administration of gadolinium contrast.
Typical Presentations of MS
The three most common presentations of MS are transverse myelitis, optic neuritis, and brainstem–cerebellar dysfunction. Acute partial transverse myelitis is “the most classic” form of transverse myelitis among patients with MS, said Dr. Pawate. Acute complete transverse myelitis, on the other hand, may be postinfectious or idiopathic, or seen as part of acute disseminated encephalomyelitis (ADEM). Similarly, longitudinally extensive transverse myelitis is more suggestive of neuromyelitis optica spectrum disorders (NMOSD) than MS.
The most typical presentation of MS optic neuritis is unilateral and has acute or subacute onset. Patients often have retrobulbar, “gritty” pain when they move their eye. Complete blindness is unusual, and complete recovery occurs in nearly all patients. Hyperacute onset suggests a vascular process rather than optic neuritis, said Dr. Pawate. Slow, insidious onset may indicate an infiltrative process such as neoplasm or sarcoidosis. Painless vision loss may indicate ischemic optic neuropathy, and severe blindness without recovery may result from NMOSD.
The most pathognomonic brainstem dysfunction in MS is intranuclear ophthalmoplegia (INO), especially when it is bilateral. Other brainstem symptoms typical of MS include ataxia, painless diplopia, facial numbness, and trigeminal neuralgia in a young patient. Hyperacute or insidious onset of brainstem symptoms is unlikely to indicate MS. Symptoms that localize to a vascular territory usually result from a stroke. In addition, multiple cranial neuropathy is more suggestive of infections such as Lyme disease, sarcoidosis, or carcinomic ulcers.
Unusual Presentations of MS
Certain variants of MS do not present with the typical periventricular ovoid lesions. Tumefactive MS often presents with a large (ie, larger than 2 cm), solitary demyelinating lesion. These lesions usually are biopsied. Treatment with steroids usually brings improvement. After this first manifestation, the patient’s course is typical of relapsing-remitting MS. “Rarely do patients have tumefactive lesions in the middle of their MS course,” said Dr. Pawate.
Another unusual presentation is concentric rings of demyelination, sometimes with mass effect. This variant is called Balo’s concentric sclerosis, and the patient may have typical MS lesions in addition to the rings. “Historically, Balo’s concentric sclerosis was thought to be a severe disease with a poor prognosis,” said Dr. Pawate. “With the advent of MRI, we know that these [rings] are more common than we initially thought, and more benign—not much different from any other MS lesions.”
Patients also may present with multiple large lesions and aggressive disease onset. Such patients need early treatment. “When I see something like this, I treat aggressively using plasma exchange and IV steroids,” said Dr. Pawate. This treatment may be followed by natalizumab infusions, and the patients may make a good recovery. “Historically, this aggressive MS onset was called Marburg variant and was fatal,” said Dr. Pawate.
MS Mimics
ADEM is more common in children than in adults, and imaging can distinguish it from MS. One distinguishing feature of ADEM is that the patient has many lesions that appear to be of the same age. Lesions may appear on the basal ganglia and the thalamus, which is atypical for MS. Spinal cord lesions tend to be longer in ADEM, compared with those in MS. ADEM tends to have a monophasic course, and patients usually present with encephalopathy, headaches, and vomiting. Patients often have a history of preceding vaccination or infection.
Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) also can mimic MS on MRI. What distinguishes it from MS are lacunar infarcts, involvement in sites like the thalamus and basal ganglia, and gray matter involvement. CADASIL affects middle-aged adults and leads to disability and dementia.
If a patient referred for suspected MS has bilaterally symmetric confluent lesions, “think more in terms of leukodystrophies,” said Dr. Pawate. The absence of gadolinium enhancement is typical in leukodystrophies. The disorders may involve the U-fibers, the brainstem, or the cerebellum, and patients may present with cognitive decline.
Susac’s syndrome is a triad of branch retinal artery occlusion, sensorineural hearing loss, and encephalopathy. The syndrome is associated with a characteristic MRI that includes “spokes” (ie, linear lesions) and “snowballs” (ie, globular lesions) in the corpus callosum, as well as a “string of pearls” (ie, microinfarcts) in the internal capsule. In the eye, the most pathognomonic finding is hyperfluorescence of the arterial wall on fluorescein angiogram. Early treatment can produce good outcomes, but missing the diagnosis may quickly result in dementia, vision loss, and hearing loss.
Lupus can cause CNS manifestations, including cerebritis, vasculitis, and myelitis. “Primary CNS vasculitis can mimic MS on MRI sometimes, but the red flags are that the patient may have headache and infarcts on MRI, which are not seen in MS,” said Dr. Pawate. The white matter lesions in neurosarcoidosis can be similar to those in MS, but neurosarcoidosis also causes leptomeningeal enhancement and cranial nerve enhancement, which are not seen in MS.
—Erik Greb