This is a basic article for medical students and other non-radiologists

Investigating focal weakness makes up a large proportion of the workload for neurologists and neuroradiologists. A wide range of serious CNS disorders can present with focal weakness. Appropriate timely imaging can guide diagnosis and treatment. 

Weakness can be due to changes in any part of the neurological system from muscle and neuromuscular junction, spinal cord or brain so history and examination are vital in guiding investigations and imaging.

Reference article

This is a summary article; there is not a more in-depth reference article.

Summary

• questions

  • is the weakness upper or lower motor neuron?

  • what is the distribution?

  • what was the speed of onset?

  • are there associated symptoms? e.g. headache, altered sensation

  • are there any co-morbidities? e.g. heart disease

  • have any other investigations been performed? e.g. lumbar puncture, nerve conduction studies/electromyography

• investigations

  • CT

    • most useful in the acute setting

    • readily available

    • able to exclude most hemorrhage and space occupying lesions

    • additional use of contrast may be performed

  • MRI

    • more sensitive than CT

    • improved contrast resolution

    • advanced imaging techniques help narrow the differential

    • lesion characterization

• making the request

  • know the question you are trying to answer

  • if the patient may be for thrombolysis (in the setting of an acute ischemic stroke), know the time of symptom onset

  • be aware of the local imaging protocol

• common pathology

  • ischemic stroke

  • intracranial hemorrhage, e.g. hemorrhagic stroke, subarachnoid hemorrhage, subdural hemorrhage, epidural hemorrhage

  • multiple sclerosis

  • intracranial tumors

  • spinal cord compression

Teaching playlist

• focal neurology