Application of the p9NORM correction method to timed neuropsychological tests in Parkinson’s disease and multiple system atrophy

Abstract

Timed neuropsychological tests do not take into account physical impairment during scoring procedures. Dysarthria and upper limb impairment can be easily measured with the PATA rate test (PRT) and the nine-hole pegboard test (9HPT). We recently validated a normalization method for timed neuropsychological tests using the PRT and 9HPT (p9NORM). We now validate the p9NORM in Parkinson’s disease (Yarnall et al. Neurology 82(4):308–316; 2014) and multiple system atrophy (MSA). We enrolled twenty-six patients with PD, eighteen patients with MSA, and fifteen healthy controls (HC). p9NORM was applied to patients with abnormal PRT and/or 9HPT. All subjects were tested with a comprehensive neuropsychological battery. No differences emerged in demographics across groups: (PD: mean age ± SD 66 ± 8; education 9 ± 4 years; MSA: age 60 ± 8; education 10 ± 4 years; HC: age 61 ± 12; education 9 ± 4 years). In MSA patients, the scores on the trail making test (TMT-A p = 0.003; TMT-B p = 0.018), attentional matrices (AM; p = 0.042), and symbol digit modalities test (SDMT p = 0.027) significantly differed following application of p9NORM. In PD patients, the TMT-A (p < 0.001), TMT-B (p = 0.001), and AM (p = 0.001) differed after correction. PD and MSA showed cognitive impairment relative to HC performance. When comparing MSA with PD, the SDMT, AM, and fluencies were similar. TMT-A and -B raw scores were different between groups (p = 0.006; p = 0.034), but these differences lost significance after p9NORM corrections (p = 0.100; p = 0.186). We confirm that the p9NORM can be successfully used in both PD and MSA patients, as it mitigates the impact of disability on timed tests, resulting in a more accurate analysis of cognitive domains.