Table 1

 Speed of onset as a clue to possible aetiology

Speed of onsetPossible aetiology
SuddenStroke, hypoglycaemia
Hours to daysInfection, Guillain–Barré syndrome, botulism
Days to weeksInfection, inflammation—for example, temporal arteritis, polymyalgia
Weeks to monthsCerebral tumours—primary or secondary
>MonthsDegenerative conditions, motor neurone disease