Nerve conduction studies (NCS)
What does a reduced conduction velocity with prolonged distal latencies suggest?
Demyelinating neuropathy
What EMG findings indicate active denervation?
Fibrillation potentials and positive sharp waves.
What is an urgent spinal MRI in sensory disturbance with a clear sensory level and upper motor neurone signs assessing for?
Spinal cord compression or myelopathy.
What are evoked potentials used to assess?
The functional conduction of specific central sensory pathways.
What CSF finding is classically associated with Guillain–Barré syndrome?
Albuminocytological dissociation — raised CSF protein with a normal or only mildly raised WCC.
What would you expect in an axonal peripheral neuropathy?
Reduced sensory nerve action potential amplitudes, with relatively preserved conduction velocity.
What does QST assess?
Sensory nerve dysfunction, especially when small fibre nerve involvement is suspected when thermal and vibration thresholds.
What MRI distribution is characteristic of multiple sclerosis?
Lesions in characteristic CNS locations including periventricular, juxtacortical/cortical and infratentorial regions, and the spinal cord.
Which evoked potential is particularly useful when investigating MS?
Visual evoked potentials (VEPs).
What CSF finding can support a diagnosis of multiple sclerosis?
CSF-specific oligoclonal bands.
What two NCS findings are particularly suggestive of demyelination rather than axonal loss?
Conduction block and temporal dispersion.
What EMG findings suggest chronic neurogenic change?
Large-amplitude, long-duration motor unit potentials with reduced recruitment.
What concept must MRI demonstrate when assessing for MS?
Dissemination in space and time, interpreted alongside the clinical picture and other investigations.
What is the advantage of VEPs in MS?
They can demonstrate subclinical optic pathway involvement.
Why can CSF be normal early in Guillain–Barré syndrome?
CSF protein may not yet have risen, particularly during the first week.
What would NCS show in carpal tunnel syndrome?
Delayed median sensory conduction across the wrist, often with prolonged median distal motor latency.
Name 3 indications for QST
Small-fibre/ painful diabetic/ idiopathic small-fibre / chemotherapy-induced neuropathy
Fabry disease
Amyloidosis
Neuropathic pain syndromes
Sjögren syndrome-associated neuropathy etc
What MRI finding suggests a thalamic cause of hemisensory loss?
An infarct or other focal lesion involving the contralateral thalamus.
What can somatosensory evoked potentials assess?
Conduction through somatosensory pathways, including central pathways affected by myelopathy or demyelination.
What is the significance of oligoclonal bands in MS?
They provide evidence of intrathecal immunoglobulin synthesis and can support dissemination in time within the appropriate diagnostic framework.
Why can NCS be normal in small-fibre neuropathy?
Routine NCS primarily assesses large myelinated fibres, whereas small fibres are not adequately assessed.
Why is QST not usually sufficient as a standalone diagnostic test?
It is psychophysical and depends on the patient's responses, so results must be interpreted with the clinical examination and other investigations.
What MRI findings might be seen in cervical myelopathy?
Cord compression with possible intramedullary T2 hyperintensity indicating cord injury.
What VEP finding supports optic pathway demyelination?
Prolonged P100 latency.
What CSF pattern would make Guillain–Barré syndrome less likely?
A substantial pleocytosis, particularly marked WCC elevation, should prompt consideration of alternative diagnoses.