Distinguishing Axonal Degeneration from Segmental Demyelination Electrophysiologically
Electrophysiological studies, like Nerve Conduction Studies (NCS), help differentiate between nerve damage patterns. The primary goal is to identify characteristic findings specific to axonal degeneration versus segmental demyelination.
Key Electrophysiological Differences:
We need to identify the statement that accurately contrasts the electrophysiological findings in axonal degeneration and segmental demyelination.
Analysis of Options:
- Option 1: Distal latency is normal in axonal degeneration and prolonged in segmental demyelination. This statement correctly identifies a key difference. Segmental demyelination significantly slows nerve impulse conduction due to myelin damage, leading to prolonged distal latencies (DL). While DL can sometimes be mildly prolonged in severe axonal degeneration, it is often normal or less affected compared to the marked prolongation seen in demyelinating processes.
- Option 2: Conduction velocity is slow in axonal degeneration and normal in segmental demyelination. This is incorrect. Conduction velocity (CV) is typically normal or only slightly slowed in axonal degeneration, whereas it is significantly slowed in segmental demyelination.
- Option 3: Conduction block is present in axonal degeneration and absent in segmental demyelination. This is incorrect. Conduction block is a hallmark of demyelinating neuropathies, not typically axonal degeneration (though severe axonal loss can reduce signal amplitude).
- Option 4: Temporal dispersion is prominent in axonal degeneration and absent in segmental demyelination. This is incorrect. Temporal dispersion (widening of the muscle response wave) occurs because different nerve fibers conduct at different speeds, which is characteristic of demyelination, not axonal degeneration.
Conclusion:
The most accurate electrophysiological distinction presented is the difference in distal latency. Segmental demyelination characteristically leads to prolonged distal latencies due to slowed conduction, while axonal degeneration typically shows normal or only mildly prolonged distal latencies, with amplitude reduction being the primary finding.
Important Questions from Neuropathies
Consider the following clinical features :
1. Hypomimia
2. Dysphonia
3. Festination gait
4. Cogwheel rigidity
Which of the features given above are generally present in Parkinsonism?
- Circuits between the basal ganglia and the motor cortex constitute the extra pyramidal system which controls muscle tone, body posture and the initiation of movement. Lesions of the extra pyramidal system present clinically with :
Consider the following statements regarding Transient Global Amnesia (TGA):
1. TGA mainly affects middle aged persons who present with abrupt, discrete loss of anterograde memory lasting for few hours.
2. During the episode, the patients are unable to record new memories resulting in repetitive questioning.
3. Consciousness is impaired during the episode and the patient is unable to perform even simple motor functions.
4. After 4-6 hours, memory function and behaviour return to normal but the patient has complete and persistent amnesia for the duration of the episode.
Which of the statements given above are correct?
- Which of the following correctly describes the primary position of the right eye in right 3rd cranial nerve palsy?
- Which of the following are correct with regard to Levodopa ?
1. It is most effective for relieving tremors
2. Only a small portion of total drug reaches the brain
3. Nausea may be offset by domperidone
4. It may trigger hallucinations
Select the correct answer using the code given below :
