Differentials
Cervical spondylosis with myelopathy and radiculopathy
SIGNS / SYMPTOMS
Presents with lower motor neuron (LMN) signs at lesion level and upper motor neuron (UMN) signs below the lesion level.
Usually has associated sensory symptoms and bladder and bowel disturbances.
INVESTIGATIONS
MRI cervical spine shows cord compression and multiple spinal root compressions.
Multifocal motor neuropathy
SIGNS / SYMPTOMS
Presents with LMN-only signs, involving one or both upper extremities.
Might begin with severe weakness in a limb without significant atrophy, with atrophy occurring later in the disease course.[46]
INVESTIGATIONS
Electrodiagnostic studies: multifocal nerve conduction block (with other locations than the usual entrapment sites). High GM1 ganglioside antibody titre (up to 80% of patients).[45]
Inclusion body myositis
SIGNS / SYMPTOMS
Slowly progressive.
Weakness affecting mainly the finger flexors and knee extensors.
There are no UMN signs.
INVESTIGATIONS
Electromyography: evidence for myopathy.
Clinical examination should not show UMN signs.
Monomelic amyotrophy
SIGNS / SYMPTOMS
Focal, predominantly LMN signs and symptoms, with usual occurrence in young people.
Commonly involves an upper extremity.
Severity of symptoms may progress over a few years while remaining limited to the initially involved limb.[47]
More frequent in Indian and Japanese populations.
INVESTIGATIONS
Clinical evaluation distinguishes this entity from ALS.
Myasthenia gravis
SIGNS / SYMPTOMS
Symptoms fluctuate.
Ocular symptoms (ptosis, diplopia, extra-ocular muscle dysfunction) are common.
UMN/LMN signs are absent.
Can mimic bulbar-onset ALS, if presents with dysphagia, dysarthria, or facial diplegia.
Weak but otherwise normal tongue in electromyography (EMG).
INVESTIGATIONS
Acetylcholine receptor or muscle-specific tyrosine kinase antibodies usually present.
Repetitive nerve stimulation may be abnormal in both conditions, but in ALS, the EMG of tongue and facial muscles shows ongoing and chronic denervation.
Benign fasciculations
SIGNS / SYMPTOMS
Focal or diffuse fasciculations, without other neurological symptoms or signs such as UMN signs, atrophy, or weakness.[48]
INVESTIGATIONS
Electromyography shows only simple fasciculations, without any motor unit potential abnormalities.
Post-polio syndrome
SIGNS / SYMPTOMS
Only LMN symptoms.
Slow progressive course.
Occurs in the segments initially involved by polio a long time after the initial viral disease.[49]
INVESTIGATIONS
Clinical evaluation distinguishes this entity from ALS.
Primary lateral sclerosis
SIGNS / SYMPTOMS
An isolated UMN disorder. Slowly progressive weakness with associated spasticity.
May convert into UMN-dominant ALS if LMN features develop over time.
INVESTIGATIONS
Serial clinical evaluation provides data for diagnosis. Electromyography excludes the LMN signs.
Progressive muscular atrophy
SIGNS / SYMPTOMS
Isolated LMN disorder.
Progressive weakness, atrophy, and fasciculation.
Some patients develop UMN symptoms and signs later during the disease course, converting into LMN-dominant ALS.[2]
INVESTIGATIONS
Serial clinical evaluations used for diagnosis.
Progressive supranuclear palsy
SIGNS / SYMPTOMS
Characteristic abnormal eye movements: slowness of vertical saccades, progressing to vertical supranuclear gaze palsy, typically causing difficulty with tasks that involve looking downwards (e.g., reading, eating, walking downstairs).
Axial-predominant (trunk and neck) symmetric parkinsonism and/or freezing of gait - with a poor response to levodopa.[50]
INVESTIGATIONS
Brain MRI typically shows significant midbrain atrophy, resulting in various diagnostic radiographical signs in the midsagittal and axial planes.[51]
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