Objective: Do median-nerve elicited blink reflex responses enable early differentiation between PD and PSP in patients with idiopathic parkinsonism?

Background: Differentiation between PD and PSP in patients with idiopathic parkinsonism is difficult at early stages, but PSP patients may show abnormal eyelid motility and reduction in acoustic startle reflexes, in spite of preserved eyelid reflexes. Based on the known brainstem pathology in PSP, Valls-Solé et al. [ref 1] reported a lack of median nerve elicited reflex responses in the orbilcularis iris muscles in combination with preserved responses in the mentalis muscles, and proposed this to be used as a diagnostic tool. However, further studies of the applicability of the test have not been reported. To this end, the present study was undertaken as a part of an extensive prospective evaluation of patients with newly debuted parkinsonism [ref 2].

Methods: A full description of the studied groups was given in [ref 2].. Median nerve stimulation was done at the ipsilateral wrist, while reflex repossess were recorded over the right mm. Orbicularis oculi and Mentalis. After a control with standard blink reflex test, three un-announced supramaximal electrical stimuli were given (100 mA; 1 ms duration), pseudo-randomly occurring with minimum 10 minutes resting interval. A positive reflex response was annotated if the EMG-signals exceeded +2SD above the reference level during minimum 10 ms, and occurring within 10 to 100 ms after the stimulus. Patient evaluation/selection and electrophysiological testing/evaluation was performed double-blinded to investigators.

Results: After careful clinical evaluation 145 PD-patients, 15 putative PSP-patients, and 31 controls were at year 1, 3 and 5. A five year follow-up time was not available for all tested subjects, as particularly patients declined the 3 and 5 year tests, due to the test being experienced as unpleasant  All controls showed normal reflex responses at start and follow up. The patient group exhibited more complex response characteristics, both at inclusion and at follow-up tests. Also the patients’ individual longitudinal changes were more variable, not necessarily showing continuous preserved or detoriorating reflex appearances.

Conclusions: As single test, the median nerve evoked blink reflex do not allow differentiation between PD and PSP in patients with early parkinsonism.

References: 1.  Valls-Solé J, Valldeoriola F, Tolosa E, Marti MJ. Distinctive abnormalities of facial reflexes in patients with progressive supranuclear palsy. Brain. 1997 Oct;120 ( Pt 10):1877–83.

2.    Linder J, Stenlund H, Forsgren L. Incidence of Parkinson’s disease and parkinsonism in northern Sweden: a population-based study. Movement disorders. 2010 Feb 14;25(3):341–8.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/do-median-nerve-evoked-blink-reflexes-allow-early-differentiation-between-pd-and-psp-in-patients-with-debuting-parkinsonism/