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Show ORIGINAL CONTRIBUTION The Ratio of Square Wave Jerk Rates to Blink Rates Distinguishes Progressive Supranuclear Palsy From Parkinson Disease Ugur E. Altiparmak, MD, Eric Eggenberger, DO, Austin Coleman, DO, and Kelly Condon, BS Background: Distinguishing progressive supranuclear palsy ( PSP) from Parkinson disease ( PD) may be difficult, particularly in the early stages, because the characteristic vertical supranuclear eye movement abnormalities of PSP may be absent or delayed until late in the course of the disease. In this study we investigated the usefulness of comparing the square wave jerk rate ( SWJR) and blink rate ( BR) in the differentiation of these two disorders. Methods: We studied 10 patients with PD ( PD group) and 5 patients with PSP ( PSP group) who met published diagnostic criteria. The SWJR and BR were measured from video recordings and were used to calculate a ratio ( SWJR: BR). Results: The PSP group exhibited a significantly higher SWJR, higher SWJR: BR, and lower BR than did the PD group. No patient with PSP exhibited a SWJR: BR of < 3; however, one patient with PD had a SWJR: BR of 5.3, creating overlap between the two groups. Conclusions: The SWJR: BR is a simple and reasonably useful clinical measure to distinguish established PSP from PD. Determining the value of this measure in differentiating early PSP from PD requires a prospective study. (/ Neuro- Ophthalmol 2006; 26: 257- 259) Progressive supranuclear palsy ( PSP) may be difficult to distinguish from Parkinson disease ( PD), especially in the early stages. Both diseases present at similar ages with extrapyramidal features, and the characteristic eye movement abnormalities of PSP are often delayed until later in its course ( 1). The different prognoses and therapeutic Departments of Neurology and Ophthalmology, Michigan State University, East Lansing, Michigan. Address correspondence to Eric Eggenberger, DO, Department of Neurology and Ophthalmology, A217 Clinical Center, 138 Service Rd., East Lansing, MI 48824- 1313; E- mail: eric. eggenberger@ ht. msu. edu management for these disorders highlight the need for early discrimination. Whereas bradykinesia with decreased blink rates ( BRs) of varying severity are common in both PSP and PD, an increased square wave jerk rate ( SWJR) is more commonly reported in PSP than in PD ( 2,3). A simple clinical measure using these ocular parameters may help to distinguish between these two conditions. To evaluate whether the BR and SWJR are useful in separating PSP from PD, we studied these measures in a small number of patients with established diagnoses of each condition. METHODS Institutional review board approval from the University Committee on Research Involving Human Subjects at Michigan State University ( MSU) was obtained for this study ( MSU number 01- 423). Patients with PD were selected according to the " possible PD" diagnostic criteria denned by Gelb et al ( 4). These required at least two of the four typical features ( resting tremor, bradykinesia, rigidity, and asymmetric onset), no features suggestive of alternative diagnoses, and a documented response to levo-dopa or a dopamine agonist. Patients with PSP ( PSP group) were selected according to the criteria denned by Lirvan et al ( 5). This category required gradually progressive onset at 40 years of age or older, vertical supranuclear palsy or slowing of vertical saccades with prominent postural instability in the first year of onset, and no evidence of another disease that could explain the clinical features. Patients with PD or PSP consented to allow videotaping of their eyes for analysis during routine visits. The tapes were reviewed to measure the SWJR and BR. The SWJR: BR was calculated and compared for the two groups. RESULTS Ten patients with PD and 5 patients with PSP were included in the study ( Table 1). We tabulated the SQJR and BR in the two groups ( Fig. 1). Then we calculated the ratios of the two rates, the SWJR: BR. We found that the SWJR: BR was significantly higher in the PSP group than in the PD group ( P = 0.004). In the PSP group, the SWJR J Neuro- Ophthalmol, Vol. 26, No. 4, 2006 257 J Neuro- Ophthalmol, Vol. 26, No. 4, 2006 Altiparmak et al TABLE 1. Patient characteristics and data Number of Subjects ( Men/ Women) Mean age ( years) Mean disease duration ( years) Mean square wave jerk rate ( SWJR) Mean blink rate ( BR) SWJR: BR Progressive supranuclear palsy 5 ( 2/ 3) 72 3 33.8 5.8 6.82 Parkinson disease 10 ( 3/ 7) 70.2 2.4 15 19.8 1.24 P value NA 0.68 0.72 0.02 0.0025 0.004 was significantly higher ( P = 0.0025) and the BR was significantly lower ( P - 0.02) than in the PD group ( Fig. 2). No patient with PSP exhibited a SWJR: BR of < 3. However, one patient with PD had a SWJR: BR of 5.3, creating an overlap between the two groups ( Fig. 2). DISCUSSION PSP is a progressive disease with fatal outcome, usually within 6- 10 years of onset ( 6,7). Early discrimination of PSP from PD is important not only for treatment options, but also for informing patients and relatives of the prognosis of the disease. Unlike PD, PSP is not responsive to any treatment. Square wave jerks ( SWJs) are thought to be caused by a temporary lapse in the inhibitory control of omnipause cells over saccadic burst neurons in the brain stem ( 8). Two probable sources of this inhibitory control are the frontal eye fields ( FEFs) and the basal ganglia. The FEFs are believed to play a major role in suppressing non- purposeful saccades through inhibition of the superior colliculus ( 9,10) and excitation of omnipause neurons in the brain stem ( 11). The basal ganglia ( substantia nigra pars reticulata) tonically suppress saccade- related cells of the superior colliculus ( 12- 14). This suppression of context- inappropriate sac-cades such as SWJs could have the adaptive advantage of helping to maintain foveation of targets of interest ( 15). SWJs are known to be a very sensitive, but nonspecific, finding in PSP, as they may be seen in low frequencies in normal older adults and are associated with multiple other neurologic disorders, including PD ( 16,17). Reflex BRs are most strongly linked to dopamine, primarily through the D2 receptors ( 2). The reduced BR in PD and PSP seems to be the result of nigrostriatal system dysfunction influencing efferent connections, including those to the superior colliculus ( 2). In this study, the BR was significantly decreased in the PSP group, consistent with prior studies ( 18,19). This pilot study re- demonstrates that SWJRs are increased in patients with established PSP ( 3) compared with patients with established PD ( 20). The study has several weaknesses, including the small number of patients and a lack of histologic proof of the diagnoses. Some of the 35 30 25 20 V) 1 15 CQ 10 OPD >::< PSP E3 S3 S3 FIG. 1. Scatter plot of square wave jerk rates ( SWJR) and blink rates ( BR) in 10 patients with Parkinson disease ( PD) and 5 patients with progressive supranuclear palsy ( PSP). 10 15 20 25 30 35 Square Wave Jerks/ min 40 45 50 258 © 2006 Lippincott Williams & Wilkins Square Wave Jerks in PSP J Neuro- Ophthalmol, Vol. 26, No. 4, 2006 14 12 10 m I 1 1 • - • - FIG. 2 . Scatter plot of ratios of square wave jerk rate ( SWJR) to blink rate ( BR) in 10 patients with Parkinson disease ( PD) and 5 patients with progressive supranuclear palsy ( PSP). 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