Rapid picture naming in Parkinson's disease using the Mobile Universal Lexicon Evaluation System (MULES)

Abstract

Objective: The Mobile Universal Lexicon Evaluation System (MULES) is a test of rapid picture naming that captures extensive brain networks, including cognitive, language and afferent/efferent visual pathways. MULES performance is slower in concussion and multiple sclerosis, conditions in which vision dysfunction is common. Visual aspects captured by the MULES may be impaired in Parkinson's disease (PD) including color discrimination, object recognition, visual processing speed, and convergence. The purpose of this study was to compare MULES time scores for a cohort of PD patients with those for a control group of participants of similar age. We also sought to examine learning effects for the MULES by comparing scores for two consecutive trials within the patient and control groups.

Methods: MULES consists of 54 colored pictures (fruits, animals, random objects). The test was administered in a cohort of PD patients and in a group of similar aged controls. Wilcoxon rank-sum tests were used to determine statistical significance for differences in MULES time scores between PD patients and controls. Spearman rank-correlation coefficients were calculated to examine the relation between MULES time scores and PD motor symptom severity (UPDRS). Learning effects were assessed using Wilcoxon rank-sum tests.

Results: Among 51 patients with PD (median age 70 years, range 52-82) and 20 disease-free control participants (median age 67 years, range 51-90), MULES scores were significantly slower (worse performance) in PD patients (median 63.2 s, range 37.3-296.3) vs. controls (median 53.9 s, range 37.5-128.6, P = .03, Wilcoxon rank-sum test). Slower MULES times were associated with increased motor symptom severity as measured by the Unified Parkinson's Disease Rating Scale, Section III (r_s = 0.37, P = .02). Learning effects were greater among patients with PD (median improvement of 14.8 s between two MULES trials) compared to controls (median 7.4 s, P = .004).

Conclusion: The MULES is a complex test of rapid picture naming that captures numerous brain pathways including an extensive visual network. MULES performance is slower in patients with PD and our study suggests an association with the degree of motor impairment. Future studies will determine the relation of MULES time scores to other modalities that test visual function and structure in PD.

Keywords: Mobile Universal Lexicon Evaluation System (MULES); Parkinson's disease (PD); Picture naming; Vision.