Motor neurone disease
Description
- Progressive degeneration of upper AND lower motor neurones
- UMN + LMN signs in the same territory, no sensory loss, no sphincter involvement, eye movements spared
- Those four negatives are what make the diagnosis
- Painless, asymmetric, focal onset that spreads to contiguous regions
Phenotypes
| % | Features | Survival | |
|---|---|---|---|
| ALS (classic) | ~70% limb onset | Mixed UMN + LMN, asymmetric; often proximal arm or asymmetric foot drop | Median 2-3 yr |
| Bulbar onset | ~25% | Dysarthria, dysphagia, tongue wasting + fasciculation | Worst - ~2 yr |
| Progressive muscular atrophy (PMA) | ~10% | LMN only, generalised or patchy onset | Longer |
| Primary lateral sclerosis (PLS) | ~10% | UMN only for >4 years, bulbar then limbs | Best - decades |
| Flail arm / flail leg | LMN-predominant, restricted for long periods | Longer | |
| Respiratory onset | 3-5% | Orthopnoea, dyspnoea, morning headache | Poor |
Bulbar vs pseudobulbar palsy - a standard exam pair
| Bulbar (LMN) | Pseudobulbar (UMN) | |
|---|---|---|
| Tongue | Wasted, fasciculating, flaccid | Small, spastic, slow ("stiff"), cannot protrude |
| Speech | Nasal, flaccid dysarthria | Strained, "Donald Duck", spastic |
| Jaw jerk | Normal or absent | Brisk |
| Gag | Absent | Brisk |
| Emotion | Normal | Emotional lability / pseudobulbar affect |
| Causes | MND, GBS, polio, brainstem infarct, myasthenia, syringobulbia | Bilateral capsular infarcts, MS, MND |
- *MND is the classic cause of a combined bulbar and pseudobulbar palsy*
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