Specific Imaging Findings

In amyotrophic lateral sclerosis (ALS) T2-weighted MR images, and particularly T2* (gradient echo), may show dark areas of increased iron deposition in the pre- and post-central gyri. This finding needs to be interpreted with caution, because it is also a part of normal aging. Increased T2 signal involving the corticospinal tracts (CSTs) from their subcortical beginning into the brainstem and medulla is characteristic. This finding should also be cautiously interpreted, as the posterior aspect of the CST travelling through the posterior limb of the internal capsule is less myelinated and may be slightly bright on T2-weighted and FLAIR images. These regions are T1 hypointense and this may be accentuated by adding magnetization transfer to the sequence. Faint linear subcortical hyperintensities on T2 sequences have been reported, particularly in the medial temporal lobes. The thickness of the primary motor cortex is reduced. The brain shows diffuse atrophy in the chronic phase, which may be more prominent in the parietal and frontotemporal regions. MRS is nonspecific and shows low NAA, creatine and glutamate; it may be used to follow the effects of treatment. DTI shows increased diffusivity and reduced volumes of the CSTs. CT shows only atrophy. MRI of the spinal cord is usually normal.

Pertinent Clinical Information

Early symptoms may be mild and nonspecific and are commonly overlooked. These include twitching, cramps and muscle stiffness or weakness. Most of the early symptoms affect the extremities, particularly the lower ones. Symptoms progress until patients are unable to walk. About a quarter of patients present with brainstem symptoms including speech and swallowing difficulties; eventually all patients lose speech and are unable to swallow. Progressive muscle weakness and atrophy may be followed by spasticity and hyperreflexia. Additional neuropsychiatric symptoms such as anxiety and depression complicate the clinical state. Some patients develop neurocognitive abnormalities similar to those encountered in frontotemporal dementia. However, in most patients cognition remains intact until death. Eye muscle control is maintained throughout life. All patients experience respiratory difficulties which require assisted ventilation. Superimposed pneumonia is a common cause of death.