Psychometrics

A study by Muller et al. (2000) found the HY scale to have good discriminant ability as subjects with PD (n = 18) showed significantly longer latencies in each HY stage than patients with atypical Parkinsonian disorder (APD; n = 63). Results of the study determined that no subject with PD progressed to stage HY-3 within 1 year, whereas 72% of those with APD did. A subsequent study of 43 PD subjects by Quelhas and Costa (2009) revealed that an HY score together with the Hospital Anxiety and Depression Scale score accounted for 42% of the variance of global quality-of-life scores, which confirmed previous studies that noted that the HY scale had stronger correlations with quality-of-life scores than other more detailed clinical assessments such as the Unified Parkinson’s Disease Rating Scale (UPDRS). A falls study by Thomas, Rogers, Amick, and Friedman (2010) of 102 persons with a median HY score of 2.5 found that the HY scale had a positive correlation with Tinetti’s Falls Efficacy Scale (FES) of 0.48 and concluded that those subjects whose gait froze more frequently used an assistive walking device, such as a cane or walker, or had more severe PD by HY stage, and exhibited greater fear of falling as measured by FES scores. A similar study of 38 men with PD found that Berg Balance Scale scores were inversely correlated with modified HY scale scores (2.48, SD 0.61; range 2 to 4) at –0.45, while the UPDRS motor scores (23.05, SD 8.48; range 9 to 43) correlated somewhat better at –0.58 (Qutubuddin et al., 2005). Finally, a study of 98 persons with PD and 31 healthy controls determined that strong correlations existed between the original HY scale and the Trunk Mobility Scale at 0.72, whereas correlations with the UPDRS motor were again somewhat better at 0.84. Both HY scales take less than 5 minutes to complete, whereas the UPDRS takes 30 minutes (Franco, Leao, Townsend, Carlos, & Rieder, 2011).

Advantages

There is a fair amount of research in support of the HY scale as a unique staging tool that can measure PD across the disease continuum. It requires no training or certifications to use in practice and its general acceptance throughout the health professions has increased communication by supporting a common language to classify the particular phenomenon witnessed in PD, thereby eliminating some barriers to treatment and participation.

Disadvantages

The Movement Disorder Society (MDS) critique of the HY scale noted that it is weighted heavily toward postural instability as the primary index of disease severity and may not capture the essence of impairments or disability from other impairment areas such as non-motor problems (Goetz et al., 2004). For example, cognitive impairment often occurs in both early and advanced stages of the disease and it has been proposed that as many as 25% of persons with PD fulfill criteria for mild cognitive impairment, which may include decreased attention, reduced executive function, as well as visuospatial and memory dysfunctions (Santangelo, Barone, Abbruzzese, Ferini-Strambi, & Antonini, 2014). The MDS critique also found that psychometric testing of the modified HY scale, which includes 0.5 increments, to be limited and suggested that without such testing the original 5-point scale should be maintained (Santangelo et al., 2014).

Administration

During assessment the clinician judges a person’s functional as well as motor performance against the inclusion/exclusion criteria of the HY scoring systems.