Diagnostic Considerations
The diagnostic criteria for primary lateral sclerosis (PLS) proposed by Pringle et al in 1992 include insidious onset of spastic paresis in adults, which usually begins in the lower extremities. [2] Affected individuals typically have no family history of similar disorders.
Some suggest that spastic paresis should be symmetrical, but asymmetrical presentation is not unusual. The paresis progresses gradually in a manner consistent with corticobulbar and corticospinal tract dysfunction. Duration should be at least 3 years, and other diagnoses should be excluded by imaging and laboratory tests.
The suggestion by Pringle et al that the diagnosis may be made within 3 years of symptom onset contradicts the 5 years' duration that was required by the criteria proposed by Stark and Moersch in 1945. [10] The criteria from Pringle et al also permit bulbar or upper extremity onset for PLS. [2]
One patient in the series of Pringle et al, who was diagnosed as having PLS by their criteria but not according to the criteria of Stark and Moersch, had bulbar onset and progressed to essentially anarthria within 2 years. This patient showed occasional fibrillation potentials in the pronator quadratus, thenar, and interosseus muscles 4 years after onset of disease. The reported follow-up (< 5 y) was the shortest in that series. This patient's course resembled that of ALS (albeit with a slower than average rate of progression) more than PLS.
Thirteen of 29 patients with upper motor neuron symptom onset reported by Gordon et al, initially diagnosed as having PLS, evolved to having upper motor neuron–dominant ALS within 3.7 years of symptom onset. Gordon et al advised a period of 4 years of observation before a patient is considered to have PLS. [3] However, in patients with bulbar onset, requiring a 5-year period of observation and greater diligence to exclude lower motor neuron involvement may be prudent before diagnosing PLS (rather than ALS).
In summary, concern for future evolution into ALS cannot be allayed by a workup shortly after symptom onset.
Lower extremity onset and slow progression (at least 3-5 y) increase confidence in the diagnosis of PLS and decrease the likelihood of a later evolution into ALS. A 5-year period of observation, without emergence of clinical lower motor neuron signs, provides greater confidence in the diagnosis than does a shorter period of observation.
From the standpoint of disease impact on patient survival and disability, rate of progression rather than diagnostic classification is the determining factor. Nevertheless, acceleration of the course may be expected if lower motor neuron signs develop in a patient who was thought to have PLS.
Go to Amyotrophic Lateral Sclerosis, Amyotrophic Lateral Sclerosis in Physical Medicine and Rehabilitation, and Emergent Treatment of Amyotrophic Lateral Sclerosis for complete information on these topics.
Other differentials
The most common causes of myelopathy in the age group in which PLS most often occurs are cervical spondylosis and chronic progressive multiple sclerosis (MS). Both are more common than PLS.
Some conditions may present initially with pure upper motor neuron dysfunction, such as progressive multifocal leukoencephalopathy (rarely without the characteristic MRI findings) or spongiform encephalopathy, but they have a rapid course that would preclude consideration of PLS.
If appropriate, also consider and exclude myelopathy associated with human immunodeficiency virus (HIV) infection.
Other disorders to consider in the differential diagnosis of PLS, aside from those in the next section, include the following conditions:
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Hereditary spastic paraparesis (HSP)
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Konzo
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Neurolathyrism
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Spinocerebellar ataxias
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Tumors of the spinal cord
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Low-grade astrocytoma
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Meningioma
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Multiple system atrophy
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Neurosyphilis
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Oligodendroglioma
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Olivopontocerebellar atrophy
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Parkinson-plus syndromes
Differential Diagnoses
