Objective: Our aim is to further understand the distinctions of PD subtypes, tremor dominant (TD) and postural instability gait disorder (PIGD), using clinical variables and instrumented analysis of gait.

Background: Parkinson’s disease (PD) can be divided into tremor dominant (TD) and postural instability gait disorder (PIGD) subtypes, with different core symptoms, and different progression and physiological underpinnings. The use of instrumented analysis of movement and gait has been helping our understanding of PD and its phenotypes, providing detailed quantitative and observer-independent data.

Methods: We have selected subjects who met criteria for idiopathic PD and that could be classified into TD or PIGD (subjects within “indeterminate” subtype were not included). Clinical data and scales were used, including, UPDRS and Freezing of gait questionnaire. Each subjects performed iTUG (instrumented Timed-Up-and-Go test) during OFF state (24h of levodopa withdrawal). The lateralization index (LI) for each variable was calculated by the absolute value of the natural logarithm of the ratio between the left side and right side performance in each measure.

Results: A total of 29 subjects were included, 16 PIGD and 13 TD. PIGD subjects had a longer disease duration and higher equivalent L-dopa drug load. Higher score in the FOG-Q was strongly associated with PIGD, forming a clear distinction of the two subtypes according to the presence and severity of freezing of gait. A multivariate logistic regression, including the iTUG as independent variables, revealed that the arms range of movement lateralization index (LI-arm RoM) significantly separates both subtypes (p-value=0.031, exp(B)=1.022, CI:1.002-1.043), although with a weak accuracy (64.3%), being higher in TD.

Conclusions: Previous studies have suggested a poorer performance of gait in PIGD patients, with longer TUG duration, slower turning and stride velocity. Our study suggested that higher LI-arm RoM correctly identifies TD, a measure implicated in larger discrepancy in range of movement between left and the right limbs, possibly due to bradykinesia of the most affected side. Also, it is possible that such asymmetry is the clinical presentation of severity of PD in TD, evident in later stages of disease and responsible for freezing of gait in this subtype. This variable may prove valuable as a disease severity marker, especially for individuals with TD subtype.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/instrumented-quantitative-study-of-movement-and-gait-in-parkinsons-disease-clinical-subtypes/