title: Normalization of middle latency auditory P1 potential following posterior ansa-pallidotomy in idiopathic Parkinson's disease.
abstract: The P1 potential (50 msec) of middle latency auditory evoked potential was evaluated in seven patients with advanced idiopathic Parkinson's disease before and after contemporaneous bilateral posterior ansa-pallidotomy. P1 potential was lacking in two patients preoperatively and was prolonged in the remainder of the patients when examined in a best medicated 'on' state. All patients showed varying degrees of dementia preoperatively on clinical examination. Remarkable improvement in their Unified Parkinson's Disease Rating Scale (UPDRS) scores during 'on' states from a mean of 45.85 to 14.28 post-operatively was achieved. Subsidence of akinetic symptoms, abolishment of dyskinesia, improvement in gait freezing, rigidity, and tremors represented main areas of improvement. P1 latencies and amplitudes reverted back to normal values in six patients including the two patients who lacked P1 wave preoperatively. One patient showed mild worsening of both Pa and P1 values post-operatively attributed to sleepiness during testing, a transient phenomenon commonly encountered following posterior ansa-pallidotomy. The post-operative P1 changes were statistically significant for both latencies and amplitudes at p = 0.078 and p = 0.073, respectively, for all seven patients using one tailed paired t-test. The change in UPDRS post-operatively best correlated with the post-operative difference in P1; specifically, UPDRS subscore II with P1 amplitude (r = -0.068, p = 0.09), and UPDRS subscore IV with Pa: P1 ratio (r = +0.77, p = 0.04). Earlier clinical and experimental work support the tegmental pedunculopontine nucleus (PPN) as the site of origin of P1 wave. In addition, its presence reflects the integrity of output cholinergic projection from PPN to both ascending reticular activating system ARAS and auditory pathway. We believe this is the first report of restoring the integrity of P1 wave following posterior ansa-pallidotomy in patients with advanced idiopathic Parkinson's disease. Disinhibition of the PPN by posterior ansa-pallidotomy can explain improvements in motor symptoms in view of reemergence and normalization of P1 wave form.
authors.affiliation: Department of Neurosurgery, Loma Linda University Medical Center, CA 92350, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Mohamed
authors.forename: R P
authors.initials: RP
authors.lastname: Iacono
authors.forename: S
authors.initials: S
authors.lastname: Yamada
mesh_terms: D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D005917:Globus Pallidus / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000209:etiology / Q000503:physiopathology* / Q000601:surgery*; D013681:Tegmentum Mesencephali / Q000502:physiology