Wednesday 25 march 3 25 /03 /Mar 14:52
Clinical History: The patient is a 45-year-old male who presents with back pain and sensory disturbance, particularly involving the left side of the body. Apparently, he has tingling sensation in the hands and feet. No medications are listed.

Details of Procedure: Visual Evoked Potential Study: Independent stimulation of the left and right eyes with pattern reversal stimuli and other stimulating recording parameters standardized for this laboratory showed definite reproducible waveforms. There was occasionally fair signal-to-noise ratio, but attempts at different trials and check sizes were performed. On left-sided stimulation, the smaller check sizes gave a P-100 potential of 119.6 msec. Higher check sizes of the same side produced a P-100 latency of 116 msec. On right-sided stimulation, there was fair signal-to-noise ratio, and even at repeated attempts, this was difficult to determine. However, the most reliable P-100 potential was measured at 144 msec. The patient has attempted to try his best, but looked tired.

Brainstem Auditory Evoked Potential Study: Independent stimulation of the left and right ears with rarefaction clicks and other stimulating and recording parameters standardized for this laboratory showed definite reproducible waveforms. On left-sided stimulation, at 100 dB interpeak latencies were as follows: I-III 2.2 msec, III-V 2.04 msec, I-V 4.24 msec. There was minimal variability in using lower intensities at 90 dB. On right-sided stimulation, this was measured as follows: I-III 2.2 msec, III-V 2.06 msec, I-V 4.26 msec. These are within normal limits.

Median Nerve Somatosensory Evoked Potential Study: Independent stimulation of the left and right median nerves with square-wave clicks and other stimulation and recording parameters standardized for this laboratory showed reproducible obligate waveforms. There was lower amplitude fair signal-to-noise ratio cervical potential, but they were still recognizable. On left-sided stimulation, interpeak latencies were as follows: Erb point to N-13 was 3.4 msec, N-13 to N-20 was 5.3 msec, Erb point to N-20 was 8.7 msec. On right-sided stimulation, the N-13 or cervical potential was still of low amplitude for definite identification. However, the most probable waveform showed the following interpeak latencies: Erb point to N-13 of 3.5 msec, N-13 to N-20 of 5.2 msec, Erb point to N-20 of 8.7 msec. These are within normal limits.
Posterior Tibial Nerve Somatosensory Evoked Potential Study: Independent stimulation of the left and right posterior tibial nerves with square-wave clicks and other stimulating and recording parameters showed definite reproducible waveforms. There was, however, fair signal-to-noise ratio on the limbal potential for definite identification. On left-sided stimulation, the amplitude of P-37 potential was measured at 42 msec. The popliteal fossa to P-37 interpeak latency was 30.6 msec. There was poor signal-to-noise ratio for definite identification of the limbal potential. On right-sided stimulation, while there was fair to signal-to-noise ratio, there was perhaps more definite reproducible limbal potential. The popliteal fossa to limbal potential interpeak latency was 11.6 msec, while the limbal potential to P-37 interpeak latency was 19 msec. The popliteal fossa to P-37 interpeak latency was 30.6 msec. The absolute P-37 latency was 41.4 msec. These are within normal limits.

Impression: Abnormal visual evoked potential study with prolongation of the P-100 potential, worse on the right than the left. Interpretation should be made with caution, since the patient was described as being tired. Nevertheless, at least for the left side, both small and large check sizes were used, and these still showed prolongation of the P-100 potential. On right-sided stimulation, almost a sinusoidal waveform was seen for definite interpretation of the lower amplitude potential. This did not identify the exact localization in the visual axis.

Normal brainstem auditory evoked potential study.

Normal median nerve somatosensory evoked potential study.

Normal posterior tibial nerve somatosensory evoked potential study.

Clinical correlation is suggested.
By VINOD NAIR
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