Motor Neuron Disease Characteristics and Diagnostic Features

Classification and Clinical Presentation

The American College of Radiology suggests that Motor neuron diseases (MND) are a group of neurodegenerative disorders characterized by the degeneration of upper motor neurons, lower motor neurons, or both, with amyotrophic lateral sclerosis (ALS) being the most common type, representing approximately 85% of all cases 1, 2, 3
Amyotrophic Lateral Sclerosis (ALS) is characterized by degeneration of both upper and lower motor neurons in the brain and spinal cord along the corticospinal tracts, with an annual incidence of 1-2/100,000 and median survival of 3-4 years after symptom onset 2, 3
Progressive Muscular Atrophy (PMA) involves degeneration of only the lower motor neurons, leading to progressive muscle weakness and atrophy without upper motor neuron signs 4
Progressive Bulbar Palsy (PBP) is a variant that primarily affects the bulbar muscles first, causing difficulties with speech, swallowing, and other functions controlled by lower cranial nerves 4
Pseudobulbar Palsy is characterized by upper motor neuron dysfunction affecting the bulbar region, causing symptoms like emotional lability, dysarthria, and dysphagia 5

ALS typically presents with a combination of hypertonicity and hyperreflexia (upper motor neuron degeneration) and muscle fasciculations, weakness, and atrophy (lower motor neuron degeneration) 2, 3
Electromyography (EMG) and nerve conduction velocity (NCV) studies are cornerstone tests for diagnosing motor neuron diseases, particularly ALS, as they can detect lower motor neuron degeneration 4
MRI of the brain without IV contrast is the optimal initial imaging modality for patients with suspected motor neuron disease, primarily to exclude other conditions with similar clinical presentations rather than to confirm the diagnosis 2, 3, 4
Common MRI findings in ALS include abnormal T2/FLAIR signal in the corticospinal tracts, particularly in the posterior limb of the internal capsule and cerebral peduncles 4
Spine MRI may show abnormal T2/STIR signal in the anterior horns ("snake eyes" appearance), though this finding is not specific for ALS and may only appear later in the disease course 3, 4

Familial ALS has clear genetic inheritance in a minority of patients, and genetic testing for ALS-associated genes (e.g., C9orf72, SOD1, FUS, TARDBP) should be considered, especially in cases with family history 4

MRI findings in anterior horn cell disorders like ALS include abnormal T2/FLAIR signal in the corticospinal tracts and abnormal hypointensity in the precentral gyrus, without involvement of sensory pathways 6
When sensory symptoms are present in a patient with suspected motor neuron disease, clinicians should consider alternative diagnoses or comorbid conditions 6

The American College of Radiology recommends MRI brain without IV contrast as the initial neuroimaging study to exclude mimics of amyotrophic lateral sclerosis (ALS), with sequences including T2/FLAIR and T2*/SWI to assess corticospinal tract hyperintensity and precentral gyrus hypointensity 7, 8, 9, 10
MRI cervical and thoracic spine without IV contrast may be appropriate to exclude structural mimics such as cervical myelopathy or syrinx, with findings including "snake eyes" appearance on T2/STIR images 7, 8, 9, 10

The revised El Escorial criteria require lower motor neuron signs, upper motor neuron signs, progressive spread within a region or to other regions, and absence of electrophysiological or pathological evidence of other disease processes 7

The American Academy of Neurology recommends multidisciplinary care for patients with ALS, including neurology, pulmonology, gastroenterology/nutrition, physical therapy, occupational therapy, speech-language pathology, social work, and palliative care, with evidence showing improved survival and quality of life 7, 8, 9
Non-invasive ventilation (NIV) is recommended for patients with ALS and respiratory insufficiency, with evidence showing improved median survival and quality of life 7, 8

In patients diagnosed with ALS, the median survival from symptom onset is approximately 3–4 years, and only about 5–10 % survive longer than 10 years. 11

Bulbar‑onset ALS accounts for roughly 25–35 % of ALS cases; it is associated with the shortest life expectancy, and around 80 % of these patients develop dysarthria and dysphagia. 11