From the Guidelines
The findings of decreased sural sensory nerve action potential (SNAP) and tibial conduction block suggest peripheral neuropathy, specifically a demyelinating polyneuropathy such as Guillain-Barré syndrome (GBS) or chronic inflammatory demyelinating polyneuropathy (CIDP). These electrophysiological abnormalities indicate damage to both sensory (sural) and motor (tibial) nerves.
Key Considerations
- The diagnosis of GBS or CIDP is supported by electrodiagnostic studies, which are helpful in confirming the diagnosis, particularly in patients with atypical presentations 1.
- The sural sparing pattern, where the sural sensory nerve action potential is normal while the median and ulnar sensory nerve action potentials are abnormal or absent, is typical for GBS 1.
- However, in this case, the decreased sural SNAP suggests a different pattern, which may indicate a more widespread neuropathy.
Treatment Recommendations
- For acute presentations like GBS, intravenous immunoglobulin (IVIG) at 2g/kg divided over 5 days or plasma exchange (5 exchanges over 2 weeks) is recommended.
- For CIDP, initial treatment includes prednisone (starting at 60mg daily with slow taper), IVIG (2g/kg loading, then 1g/kg every 3 weeks), or both.
- Supportive care is essential, including physical therapy, pain management with gabapentin (300-1200mg three times daily) or pregabalin (75-300mg twice daily), and monitoring for respiratory compromise in acute cases.
- Regular follow-up with nerve conduction studies every 3-6 months helps assess treatment response and disease progression. Note that the evidence from 1 and 1 is not directly relevant to the diagnosis and treatment of peripheral neuropathy with decreased sural SNAP and tibial conduction block, and therefore is not considered in this recommendation.
From the Research
Sural Decreased Snap and Tibial Conduction Block
- The sural nerve is often affected in patients with peripheral neuropathy, with decreased snap being a common finding 2.
- Tibial conduction block is also a common feature of peripheral neuropathy, particularly in patients with diabetic neuropathy 3.
- Nerve conduction studies (NCS) are an important diagnostic tool for assessing peripheral neuropathy, with the sural and tibial nerves being commonly tested 2, 3.
- The presence of abnormal nerve conduction parameters, such as decreased sural snap and tibial conduction block, can be indicative of underlying neuropathy 2, 3.
- Treatment options for peripheral neuropathy, such as gabapentin and B vitamins, may help to alleviate symptoms and improve nerve function 4, 5, 6.
Diagnostic Strategies
- A strategy starting with tibial and sural NCS on one side is recommended for electrophysiological screening for distal symmetric polyneuropathy 2.
- If one of these nerves is abnormal, examining the other lower and upper extremity nerves, including distal sensory nerves, is recommended 2.
- At least two abnormal nerves are recommended for a diagnosis of polyneuropathy, preferentially including the sural nerve 2.
Treatment Options
- Gabapentin is a commonly used treatment for peripheral neuropathy, particularly for painful diabetic neuropathy 4, 6.
- B vitamins, such as thiamine and cyanocobalamine, may also be effective in treating peripheral neuropathy, particularly when combined with gabapentin 5, 6.
- Pregabalin is another treatment option for peripheral neuropathy, although it may have a higher risk of adverse effects, such as vertigo and dizziness, compared to gabapentin and B vitamins 6.