= Lou Gehrig's disease (famous baseball player for NY Yankees)

= most common form of motor neuron disease (without autonomic / sensory / cognitive involvement)

Cause: free radical damage to neurons / autoimmune process / heavy metal toxicity

Age: middle – late adulthood; M >F

Path: atrophy of precentral gyrus

Histo: loss of pyramidal + Betz cells in motor cortex; loss of anterior horn cells in spinal cord; swelling of proximal axons of neuronal cells

• progressive neurodegenerative disorder
• upper neuronal symptoms: hyperreflexia, spasticity
• lower neuronal symptoms: fasciculation, atrophy

MR:

• hyperintense corticospinal tracts (corona radiata, corpus callosum, posterior limb of internal capsule, ventral aspect of brain stem, anterolateral column of spinal cord) on T2WI
• low SI in motor cortex on T2WI ← iron deposition

DDx: Friedreich ataxia, vitamin B₁₂ deficiency (abnormal signal limited to internal capsule)