Abstract
The cutaneous silent period (CSP) is a spinal inhibitory reflex primarily mediated by A-delta fibers. Prolonged CSPs have been reported in patients with restless legs syndrome (RLS) and idiopathic Parkinson's disease (IPD). Dopaminergic medication normalizes the CSP, concurring with the effect of levodopa on CSPs. To date, CSPs have not been extensively studied in patients with multiple system atrophy (MSA). The purpose of this study was to confirm abnormal CSP findings in a group of MSA patients and to affirm the lack of influence of levodopa on CSPs during long-term treatment. We investigated 15 patients (4 males, 11 females, age 58-71 years) who fulfilled the diagnostic criteria for possible MSA. Thirteen patients had predominant parkinsonian symptoms (MSA-P), 2 had predominant cerebellar signs (MSA-C). We recorded CSPs in thenar muscles following noxious digit II stimulation. Sixteen healthy volunteers (6 males, 10 females, range 24-56 years) served as control subjects for CSP recordings. Group average CSP onset was mildly delayed (P<0.01), whereas CSP end latency (P<0.001) were markedly delayed and CSP duration prolonged (P<0.001) in MSA patients compared to healthy controls. MSA patients on levodopa treatment did not differ in their CSPs from those without levodopa. The dose of levodopa did not correlate to any CSP parameter. The observed CSP prolongation corroborates previous findings in a limited number of MSA patients. The ineffectiveness of long-term levodopa on CSP abnormalities is consistent with its poor clinical effect in MSA.
Highlights
Multiple system atrophy (MSA) is a sporadic and progressive neurodegenerative disorder characterized by autonomic failure in combination with parkinsonism or cerebellar ataxia
Nine patients were on levodopa treatment with an average of 897 mg/d
MSA is a rare progressive neurodegenerative disorder presenting with extrapyramidal, cerebellar, pyramidal and autonomic signs
Summary
Multiple system atrophy (MSA) is a sporadic and progressive neurodegenerative disorder characterized by autonomic failure in combination with parkinsonism or cerebellar ataxia. Cutaneous nerve electrical stimulation produces transient suppression of electromyographic (EMG) activity in a voluntarily contracted muscle in the same extremity, known as the cutaneous silent period (CSP) (ref.[12,13]). The afferent nerve fibers mediating the CSP are slowlyconducting A-delta fibers[13,14]. The exact neural mechanism of inhibition has yet to be elucidated; the CSP could be evoked either by postsynaptic inhibition of the motoneuron itself or through presynaptic inhibition of excitatory inputs to those motoneurons which sustain the voluntary contraction[12,15]. Several characteristics of the CSP depend on physiological parameters, e.g. the combination of nerve stimulated and muscle recorded from[13]
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