The definition of weakness is important, because many patients who self-describe a ‘weak limb’ will actually have a clumsy limb (ataxia), a numb limb (reduced sensation), or a limb that is too painful to move. The time course of the onset of the symptoms in general reflects the time course of the underlying pathology: • Sudden onset (seconds to minutes) usually implies either trauma (e.g. displaced vertebral fractures due to major trauma) or certain vascular insults (e.g. stroke, transient ischaemic attack (TIA)). • Subacute onset (hours to days) suggests a progressive demyelination (e.g. Guillain–Barre syndrome, multiple sclerosis) or a slowly expanding haematoma (e.g. subdural haematoma). • Chronic onset (weeks to months), is consistent with pathologies such as a slow-growing tumour or motor neuron disease (progressive degeneration of motor neurons). As only acute and subacute limb weakness will present acutely to generalists in hospital (chronic onset cases will most likely be referred to neurology from primary care), we have limited the chapter to these cases. Limb movement requires an intact pathway from the cerebral cortex, down the corona radiata, internal capsule, and pons, along the corticospinal tract of the spinal cord, out along a nerve root, and down a peripheral nerve to the neuromuscular junction and muscle itself. If a patient has limb weakness, there must be a lesion somewhere in this pathway. Figure 26.2 gives the differential diagnosis for limb weakness. Mr Walker has presented with rapid onset of left-sided arm weakness. Key clues in the history to elicit include: • Exact time of onset? This is critical in suspected strokes because the window of time in which to confirm the diagnosis and administer thrombolysis (if appropriate) is only 4.5 hours from onset of symptoms (after that, you risk doing more harm than good to the patient). If you suspect a stroke in a patient within that time frame, call the thrombolysis team immediately. In this case, all we can say is that the onset was at some point in the 7 hours between 11 p.m. (when he went to sleep) and 6 a.m. (when he woke up), so we cannot confidently say the onset was within 4.5 hours.
More rapid intensification of flash droughts with shorter onset timescales
