Neuroradiology Case of the Week

Case 44

Ramon de Guzman, MD, P-L Westesson, MD, PhD, DDS
and Sven Ekholm, MD, PhD

Clinical Presentation: A previously healthy 27-year-old male presents with progressive dysarthria, dysphagia, and weakness.

Radiological Findings:
MR Findings: White matter hyperintensities were seen in both precentral gyri extending down along the corticospinal tracts. These changes were visualized as far down as the peduncles of mesencephalon, seen on diffusion, FLAIR as well as T2-weighted images.
Besides these findings was noted a decreased signal intensity along the precentral gyri on gradient echo images.

Figure 1A	Figure 1B
Figure 1: Axial DW image shows hyperintensities within the corticospinal tracts of the posterior limb of the internal capsules (arrows). On the FLAIR sequence there is high signal within the precentral gyri of bilateral hemispheres (arrows).
Figure 2. Coronal T2-weighted image shows hyperintensities along the corticospinal tracts (arrows).

Diagnosis: Amyotrophic lateral sclerosis.

Discussion:
Clinical Discussion
   ALS is sometimes called Lou Gehrig’s disease after a baseball player of the New York Yankees. Gehrig made this a familiar disease to the general population in 1939 when he benched himself because of loss of motor control.
   Amyotrophic lateral sclerosis (ALS) is a progressive neuromuscular disorder characterized by degeneration of motor neuron cells in the brain (upper motor neurons) and spinal cord (lower motor neurons) that control voluntary muscles resulting in paralysis and eventually death. The start of ALS can be subtle with initial symptoms being weakness in affected muscles which later spreads to other parts of the body. ALS is also characterized by muscle wasting, fasciculation, and hyperreflexia. Disease progression is relentless. Most patients die from respiratory failure and half of them are dead within 3 years, and 90% by 6 years following symptom onset [1].
   ALS affects as many as 20-30,000 Americans at any given time with as many as 5000 diagnosed every year in the US. Age at the time of symptom debut is usually between 40 to 70 years of age. Most cases, 90-95% occur at random, but in 5-10% of the cases there is a family history of ALS.
   ALS primarily involves anterior horn cells in the spinal cord and cranial motor nerves. Patients may show weakness of bulbar muscles, or of single or multiple limb muscle groups. Presentation is not always bilateral or symmetrical. A predominantly bulbar form usually leads to more rapid deterioration and death. Limb weakness is predominantly distal, and weakness and atrophy of the intrinsic hand muscles are often prominent. The common path of disease progression involves the forearm and shoulder girdle muscles, and the lower extremities. ALS rarely affects cognitive functions. Electromyogram (EMG) shows signs of diffuse denervation with generally preserved nerve conduction velocities. Although an inflammatory process may be present, new evidence points toward multiple mechanisms that promote neuronal cell death in the CNS as the underlying basis for ALS. The recent demonstration of superoxide dismutase 1 (SOD1) mutations in human familial ALS and in murine ALS models supports the view that oxidative stress, mitochondrial dysfunction and excitotoxic pathways may be involved in the process of neuronal cell death [2].

Neuro Imaging Discussion
   There is no definitive diagnostic test for the disease and there is no established technique to demonstrate upper motor neuron involvement except for the neurological examination.
   The initial focus was on MR imaging features such as hyperintensity in the corticospinal tracts. However, this is often a late finding and is demonstrated in less than half of the patients clinically diagnosed with ALS. T2-weighted MR scans disclose high signal areas along the large myelinated pyramidal tract fibers in the posterior limb of the internal capsule and cerebral peduncles in about 25% of cases(3).
   MR spectroscopy studies are underway, but at present CT and MRI are used to rule out other disease entities which may have a similar presentation.

References:

1. Braffman, BH, Trojanowski JQ, Atlas SW: The aging brain and neurodegenerative disorders. In Atlas SW, editor, Magnetic Resonance Imaging of the brain and spine, pp. 567-624, New York, Raven Press, 1991.
2. Dangond F. Amyotrophic lateral sclerosis. EMedicine. January 2002.
3. Osborn, A: Acquire Metabolic, White Matter, and Degenerative Diseases of the Brain. In Osborn A, editor, Diagnostic Neuroradiology, pp748-781, St. Louis, Missouri, Mosby 1994.