EHR525: Exercise Prescription for Motor Neuron Disease (ALS)

Comprehensive vocabulary flashcards covering the pathophysiology, phenotypes, diagnostic signs, staging, pharmacological treatment, and exercise prescription contraindications for Motor Neuron Disease and Amyotrophic Lateral Sclerosis (ALS).

Motor Neuron Diseases (MNDs)

A group of neurological conditions characterised by the progressive degeneration of upper motor neurons, lower motor neurons, or both, leading to muscle atrophy, weakness, and progressive loss of function.

Upper Motor Neurons (UMNs)

Motor neurons with cell bodies located in the motor cortex whose axons travel through the corticospinal tract to innervate the anterior horn cells of the spinal cord.

Lower Motor Neurons (LMNs)

Motor neurons with cell bodies located in the anterior horn of the spinal cord whose axons exit the central nervous system to directly innervate skeletal muscle fibres.

Amyotrophic Lateral Sclerosis (ALS)

The most common MND phenotype (accounting for $80\%$ of cases), characterised by both upper and lower motor neuron involvement, rapid progression, and an average survival of $2\text{--}5\text{ years}$ from symptom onset.

Progressive Bulbar Palsy

An MND phenotype accounting for $15\%$ of cases, characterised exclusively by bulbar (brainstem and cranial nerve, such as CN X vagus) involvement, affecting speech, swallowing, and chewing, with rapid progression and a $1\text{--}3\text{ year}$ survival.

Progressive Muscular Atrophy

A rare MND phenotype accounting for $4\%$ of cases, characterized exclusively by lower motor neuron degeneration affecting the limbs, trunk, and respiratory muscles, with moderate progression and a $5\text{--}10\text{ year}$ survival.

Primary Lateral Sclerosis

A very rare MND phenotype ($1\text{--}4\%$ of cases) involving upper motor neurons only, resulting in spasticity, coordination deficits, and balance issues, with a slow progression and a $10\text{--}20\text{ year}$ survival.

Pyramidal Pattern of Weakness

A pattern of weakness typical of upper motor neuron lesions where extensors are weaker than flexors in the upper limbs, while flexors are weaker than extensors in the lower limbs.

Clinical Signs of UMN Lesions

Manifestations of central motor pathway damage that include muscle weakness, hypertonia (spasticity or rigidity), hyperreflexia, contractures, disuse atrophy, and pyramidal weakness patterns without fasciculations.

Clinical Signs of LMN Lesions

Manifestations of peripheral motor pathway damage that include flaccidity or hypotonia, reduced or absent reflexes (hyporeflexia), marked neurogenic muscle atrophy, and visible muscle fasciculations.

Pathological Hallmarks of ALS

Degeneration and death of pyramidal cells in the motor cortex, ventral horn cells of the spinal cord, and lower cranial motor nuclei of the brainstem, accompanied by fibrous glial cell proliferation replacing lost neurons.

Pre-symptomatic Motor Neuron Loss in ALS

The clinical reality that up to $50\%$ of motor neurons may already be destroyed before an individual notices and reports functional motor deficits.

Riluzole

The only pharmacological agent proven to prolong overall survival and slow symptom progression in ALS, acting by suppressing glutamate neurotransmission to reduce excitotoxicity.

Motor Unit Remodelling on EMG

An electromyographic finding characterized by fewer, but larger-amplitude spikes, indicating collateral reinnervation of orphaned muscle fibres following lower motor neuron death.

Absence of EMG Silent Period

The loss of electrical silence following an evoked motor potential on surface EMG, indicating loss of descending lower motor neuron inhibition due to upper motor neuron degeneration.

Early-Stage ALS

The stage spanning $0\text{--}2\text{ years}$ from onset, presenting with mild focal muscle weakness, minor atrophy, twitches, cramping, and preserved independence in activities of daily living.

Middle-Stage ALS

The stage spanning $2\text{--}4\text{ years}$ from onset, characterized by increased weakness and atrophy, paralysis of some muscles, the potential need for mobility or communication aids, and early breathing difficulties.

Late-Stage ALS

The stage spanning $4\text{--}6\text{ years}$ from onset, characterized by severe muscle atrophy, severely limited mobility, dependency for most daily activities, feeding tube requirement, and emerging respiratory insufficiency.

End-Stage ALS

The final stage occurring $5+\text{ years}$ from onset, characterized by near-total voluntary muscle paralysis, high dependency for care, hospice care requirement, and severe respiratory compromise as the primary cause of mortality.

Breath Stacking

A respiratory therapy method involving taking consecutive small breaths without exhaling between them, designed to achieve fuller lung inflation and maintain chest wall compliance.

Resistance Training Red Flags in ALS

Absolute safety guidelines requiring the avoidance of heavy loads ($\le 65\%$ of $1\text{RM}$; perceived exertion $\le 6/10\text{ RPE}$), complete avoidance of eccentric actions, and omitting muscles that lack antigravity strength.

Aerobic Exercise Red Flags in ALS

Absolute safety limits requiring the avoidance of continuous sessions longer than $20\text{ minutes}$, preventing respiratory overexertion (dyspnoea rating kept $\le 4/10$), avoiding high-impact activities, and using low-fall-risk modalities.