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Introduction: The present study is an examination of possible
subclinical involvement of lower motor neuron (LMN) in patients with
primary lateral sclerosis (PLS) and hereditary spastic paraparesis (HSP)
electrophysiologically.
Methods: Nine PLS patients and 5 HSP patients were prospectively
analyzed. Jitter measurement with concentric needle electrode (25
mm, 30 G) (CN-jitter) recorded from right extensor digitorum muscle
during voluntary contraction with 1 kHz high-pass frequency filter set.
European Myelopathy Score (EMS) was used to evaluate disability. The
relationship between disability score and jitter values was investigated.
Results: HSP patients had suffered from the disease for longer period
of time (p<0.001). Mean jitter values of patients with PLS and HSP were
26.5±12.1 µs and 30.8±34.8 µs, and the number of individual high jitters
(>43 microseconds) observed in the PLS and HSP groups was 16/180
and 9/100, respectively without a significant intergroup difference. The
ratio of patients with an abnormal jitter study were higher in HSP group
(60%) compared to PLS (22%) (p<0.05). Potential pairs with blocking
were present in HSP group (7 of 100 potential pairs) but not seen in PLS
patients. EMS values were significantly lower in patients having potential
pairs with high jitter and blocking compared to those without high jitter
and blocking.
Conclusion: The present study has demonstrated that early signs of
LMN dysfunction can be detected electrophysiologically by CN-jitter
in patients with UMN involvement. These electrophysiological findings
in these patients with longer disease duration and lower clinical scores
may be explained by spreading of the disease to LMNs or transsynaptic
degeneration and its contribution in disease progression.
Keywords: Transsynaptic degeneration, primary lateral sclerosis,
hereditary spastic paraparesis, jitter