KYOTO, Japan — The R2 component of the blink reflex recovery cycle (R2 BRRC) appears to be a useful tool to distinguish progressive supranuclear palsy (PSP) from corticobasal degeneration (CBD) with high sensitivity and specificity when the differential diagnosis is in question because of an overlap of clinical features.
R2 BRRC is an electrophysiologic measure of the excitability of brainstem interneurons. PSP usually presents with supranuclear vertical gaze palsy and symmetric parkinsonism, whereas CBD usually shows cortical sensory loss and asymmetric parkinsonism.
“However, a small percentage of CBD patients could present with clinical symptoms that are characteristic of PSP patients, especially at the early stage of the disease,” Giorgia Sciacca, MD, from the University of Catania, Italy, told delegates here at the XXIIIWorld Congress of Neurology (WCN). “So the differential diagnosis between the disorders is not so simple.”
In a trial to determine the sensitivity, specificity, and positive and negative predictive values of the R2 BRRC to distinguish PSP from CBD, neurologists blinded to the electrophysiologic assessment diagnosed PSP (n = 12) and CBD (n = 8) by using accepted criteria for each condition, and the neurophysiologist was blinded to those assessments.
The trial also included 10 healthy controls. Clinical evaluation included Hoehn and Yahr stage and the Unified Parkinson’s Disease Rating Scale–Motor Examination section (UPDRS-ME).
The blink reflex was assessed by external electrode stimulation of the supraorbital nerve in its foramen for 0.2 milliseconds with an intensity of 15 mA to 50 mA. Bilateral electromyography simultaneously recorded responses of both orbicularis oculi muscles.
Paired stimuli were applied with interstimulus intervals (ISIs) ranging from 100 to 750 milliseconds, separated by time intervals of 15 to 30 seconds to minimize habituation. R2 amplitude ratios were the R2 peak-to-peak amplitude of the conditioned response (percentage) divided by the R2 peak-to-peak amplitude of the unconditioned response (percentage) for each ISI, which were then plotted vs all the tested ISIs.
PSP and CBD patients and controls had a mean age range of 64 to 71 years. Disease duration was 5.4 years for PSP and 3.4 years for CBD. The only significant difference in clinical characteristics between the PSP and CBD groups were in the UPDRS-ME scores (41.1 ± 12.9 vs 27.6 ± 13.9, respectively; P = .04) and the Hoehn and Yahr scores (3.5 ± 1.0 vs 2.3 ± 1.2; P = .02).
R2 BRRC Findings
“There was a statistically significant difference in terms of R2 amplitude from a stimulus interval of 100 ms to stimulus interval of 300 ms between PSP and CBD patients but also between PSP and controls,” Dr Sciacca said. “There were no statistically significant trends between CBD and the controls.”
Table. R2 Blink Reflex Recovery Cycle Ratios
| ISS (ms) | Patients With PSP (n = 12) (%) | Patients With CBD (n = 8) (%) | Healthy Controls (n = 10) (%) | P Value (PSP vs CBD) | P Value (PSP vs Control) | P Value (CBD vs Control) |
|---|---|---|---|---|---|---|
| 100 | 59.4 ± 35.8 | 11.1 ± 31.5 | 0 | .006 | <.001 | 0.3 |
| 150 | 59.6 ± 23.6 | 6.4 ± 18.0 | 0.9 ± 2.8 | <.001 | <.001 | 0.3 |
| 200 | 70.5 ± 30.4 | 6.5 ± 18.4 | 4.9 ± 8.3 | <.001 | <.001 | 0.8 |
| 300 | 72.2 ± 30.3 | 32.7 ± 40.2 | 27.9 ± 14.8 | .02 | <.001 | 0.7 |
For the presence of an early recovery of the R2 BRRC in detecting PSP vs CBD, the researchers calculated a sensitivity of 91.7% (95% confidence interval [CI], 61.5% – 99.8%) and a specificity of 87.5% (95% CI, 47.3% – 99.7%).
The positive predictive value was 91.7% (95% CI, 61.5% – 99.7%), and the negative predictive value was 87.5% (95% CI, 47.4% – 99.7%).
PSP and CBD “belong to a common neuropathological entity,” Dr Sciacca said, “but peculiar characteristics can be identified to distinguish the two disorders.” She said that “the predominant brainstem 4-repeat-tau aggregates distribution in PSP, in contrast with the involvement of the neocortex in CBD, could explain the brainstem disinhibition observed in PSP patients.”
She concluded that R2 BRRC “might be considered a useful tool in differentiating PSP from CBD.”
Session co-chair Chandrashekkar Meshram, MBBS, MD, DM, director of the Brain and Mind Institute in Nagpur, India, agreed. He said that the R2 BRRC is routinely used clinically as one aspect of a diagnosis of certain movement disorders, “but this was differentiating between PSP and corticobasal degeneration [and] this was a new finding.”
There was no commercial funding for the study. Dr Sciacca and Dr Meshram have disclosed no relevant financial relationships.
XXIII World Congress of Neurology (WCN). Abstract 212. Presented September 17, 2017.
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