UTMJ Imaging Case Presentation: Number 1. PART II
The Diagnosis is Amyotrophic lateral sclerosis (ALS).
Overview
Amyotrophic lateral sclerosis (ALS) is the most common neurodegenerative disease of the motor neuron system resulting in progressive muscle weakness and wasting. It is also known as Charcot’s disease or Lou Gehrig disease. The etiology is unknown. The incidence of ALS is 1.5-2/ 100 000 per year with a prevalence of 3-8/100 000 (1, 2).  Disease onset is typically in the 5-6th decade with males more commonly affected. ALS most commonly is a sporadic disease although familial ALS does occur in 5-10 % of patients (3).
Clinical Features
The clinical features of ALS involve both upper motor neuron (UMN) and lower motor neuron (LMN) signs without sensory or autonomic symptoms. Post-mortem examination typically shows the brain to be macroscopically normal. Some cases reveal atrophy of the precentral gyrus. Microscopy shows profound neurodegeneration in the brain and the spinal cord. The UMN findings of hyperreflexia and spasticity result from loss of pyramidal cells in the motor cortex, gliosis in layers II and III and degeneration of the lateral corticospinal tract (4), which are hardened to palpation at autopsy, hence the term "lateral sclerosis." The LMN findings of weakness, atrophy, and fasciculations are a direct consequence of muscle denervation, hence the term "amyotrophic."
Imaging studies
The MRI features of ALS are fairly specific. Abnormal high signal is noted in the corticospinal tract on T2 (panels A-E), proton density and susceptibility weighted imaging (panel F). The signal change will be seen to involve the coronal radiate and extends inferiorly through the posterior 1/3 of the posterior limb of the internal capsule and then into the cerebral peduncles. Gradient imaging will show low signal within the cortex of the precentral gyrus. This may reflect the deposition of iron and heavy metals (5).

Management
There is no cure for ALS. Patients gradually develop muscle atrophy and weakness. Respiratory failure is the most common cause of death. Riluzole, a glutamate release inhibitor is the only medication that has been shown to prolong trachestomy-free survival. Symptomatic management is the mainstay of treatment for ALS. As ALS progresses, the goal of patient care changes from maximizing function to providing palliative care. The mean survival for patients is approximately 3-4 years after the onset of focal weakness.
Conclusion
This patient’s combination of upper motor neuron clinical findings and lower motor neuron electrophysiological findings was very suggestive of a diagnosis of ALS. However, the EMG findings were insufficient to fulfill the lower motor neuron criteria for ALS. Moreover, a cervical radiculomyelopathy and lumbar polyradiculopathy could theoretically present with similar findings. The MRI of the brain strongly supported the clinical diagnosis of ALS and significantly aided in the patient’s diagnosis.

References

1. Logroscino G, Traynor BJ, Hardiman O et al. Incidence of amyotrophic lateral sclerosis in Europe. J Neurol Neurosurg Psychiatry 2010: 81: 385-390.
2. Worms PM. The epidemiology of motor neuron diseases: a review of recent studies. J Neurol Sci 2001: 191: 3-9.
3. Baek WS, Desai NP.ALS: pitfalls in the diagnosis. Pract Neurol. 2007 Apr;7(2):74-81.
4. Comi G, Rovaris M, Leocani L. Review neuroimaging in amyotrophic lateral sclerosis. Eur J Neurol. 1999 Nov; 6(6):629-37. Review.
5. Cheung G, Gawel MJ, Cooper PW, Farb RI, Ang LC, Gawal MJ. Amyotrophic lateral sclerosis: correlation of clinical and MR imaging findings. Radiology. 1995 Jan;194(1):263-70. Erratum in: Radiology 1995 Sep;196(3):800.

Authors
Kun Huang - University of Toronto, Medical Student Candidate, 1T3
Liping Lin, MD – Department of Neurology, St. Michael’s Hospital, University of Toronto
Eric Bartlett, MD – Department of Medical Imaging, University Health Network,         University of Toronto
Eugene Yu, MD – Department of Medical Imaging, University Health Network, University of Toronto