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Abstract

Eye drop test for diagnosis of Parkinson disease (PD)


Recent studies have shown that cardiac sympathetic innervation is reduced in patients with PD.1,2 Sawada et al3 postulated that sympathetic innervation to the pupillary dilator muscle in PD may be reduced because it is innervated by the cervical sympathetic ganglia. They studied sympathetic dysfunction in the pupils as a possible diagnostic marker of PD by comparing responses to cocaine eye drops and phenylephrine eye drops. Cocaine blocks norepinephrine uptake, and cocaine-induced mydriasis is dependent on the sympathetic nerve terminal density. In contrast, phenylephrine acts directly on the adrenergic receptor to cause mydriasis. Thirty eight patients with PD, 20 age-matched controls (with no evidence of neurologic disease) and 10 patients with multisystem atrophy (MSA) were enrolled. Cocaine-induced mydriasis in patients with PD was significantly less than that in the control and MSA groups while there was no significant difference between the control and MSA groups. The three groups did not differ in phenylephrine-induced mydriasis. The mean difference between phenylephrine- and cocaine-induced mydriasis was significantly greater in the PD group than in the control and MSA groups. Using a cutoff point of 1.0 mm, the sensitivity and specificity of phenylephrine- and cocaine-induced mydriasis difference for the diagnosis of PD were 0.80 (95% CI, 0.65-0.94) and 0.79 (95% CI, 0.67-0.94), respectively (3). Although eye drop tests can be affected by several factors, including corneal permeability and age, these variations are consistent within an individual patient, and the difference between phenylephrine- and cocaine-induced mydriasis can be a good measure of pupillary sympathetic innervation. However, these results need to be replicated before this simple test can be touted as the first diagnostic test for PD. 1. Orimo S, Ozawa E, Nakade S. (123) I-metaiodobenzylguanidine myocardial scintigraphy in Parkinson's disease. J Neurol Neurosurg Psychiatry 1999; 67:189-94.2. Takatsu H, Nagashima K, Murase M. Differentiating Parkinson disease from multi-system atrophy by measuring cardiac iodine-123 metaiodobenzylguanidine accumulation. JAMA 2000;284:44-5.3. Sawada H, Yamakawa K, Yamakado H.. Cocaine and phenylephrine eye drop test for Parkinson disease. JAMA 2005; 293:932-4.