Objective: To investigate whether changes over time in cognitive and motor functions differ across the postural instability gait difficulty (PIGD) and tremor dominant (TD) motor sub-types.

Background: Parkinson’s disease (PD) is traditionally classified into PIGD and TD motor sub-types. Mild cognitive deficits are increasingly recognized as a common non-motor symptom in PD, however, cognitive differences among those two motor sub-types have not been well-described.

Methods: Non-demented patients with PD who were previously classified into PIGD (n=30) and TD (n=27) were followed for an average of 60 months. At baseline and at follow-up, participants underwent cognitive testing using the Montreal Cognitive Assessment (MoCA), and a computerized neuropsychological assessment battery (NeuroTrax™). Parkinsonian motor symptoms using the motor part of the UPDRS, gait under single and dual task conditions, the Timed up and Go (TUG) and the Berg Balance test were also evaluated.

Results: At baseline, the two sub-types were similar with respect to age (p=0.652), disease duration (p=0.628), UPDRS-III  (p=0.328),  and all cognitive functions (p>0.29). The Berg balance test was significantly lower in the PIGD group (p=0.007).  At follow-up, basic characteristics, e.g., age, gender, disease duration were similar in the PIGD and TD. The global cognitive score declined by 9.5% in the PIGD group (from: 94.5±11.7 to 85.3±13.6, p<0.001), significantly larger (p=0.03) than the 4.5% decrease observed in the TD group, resulting in a significant group x time effect (p=0.047).  Similar group differences (p=0.006) were observed in the decline of executive function, where a significant group x time effect was also found (p=0.002). Regarding motor aspects, there was a significant deterioration in the UPDRS-III, gait features and balance in both sub-types, but no interaction effect.

Conclusions: In both sub-types, development of clinically significant gait and balance problems were associated with disease progression. Conversely, the course of cognitive decline differed. These findings demonstrate that PIGD patients experience greater cognitive decline, compared to patients with TD, in specific domains of cognitive function, suggesting that perhaps certain treatments should be tailored more precisely to the motor sub-type.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/is-cognitive-decline-similar-among-parkinsons-disease-motor-sub-types-a-prospective-study-examining-changes-over-time-in-gait-balance-and-cognition/