Medication non-adherence in PD is widespread and has adverse clinical consequences. Despite increased susceptibility to cognitive impairment and subsequent functional decline, this is the first study to examine the cognitive correlates of the ability to understand and implement medication management in PD. There are several notable findings from this study. Foremost, over half (54%) of the present sample was unable to successfully complete the HMS schedule and pillbox (i.e., scored less than 80% on both components) despite only 23% of the sample reporting difficulty with medication management and most scoring in the normal range on a commonly used cognitive screening measure (i.e., MoCA). This figure of medication management difficulty on the HMS corresponds to findings from Leopold et al. (2004)
who found 53.8% of adults with PD took medications on the wrong days or at the wrong time. Our work differs from Leopold et al. (2004)
and other investigators in that we used the HMS to measure adherence, as opposed to an electronic pill bottle monitoring system. Although such electronic monitoring systems assess compliance in real life situations, they are expensive, impractical, and fail to consider whether the patient has the ability to understand medication management (Bainbridge & Ruscin, 2009
). Results from the present study suggest the HMS may be a more cost efficient alternative of medication adherence measurement while also capturing the more complex ability to manage medications.
The second implication of this work is that, in our sample of participants with PD, the ability to understand and implement medication management was strongly related to performance on standard measures of verbal learning and recall, cognitive flexibility, and problem solving. Large standardized mean differences (d) were observed between performances on the HVLT-R, WCST-64, Digit Span, and Trails A when comparing participants who successfully completed the HMS to those who did not. The magnitude of these differences is remarkable considering the cognitive abilities of those participants unable to successfully complete the HMS remained largely intact based on published normative data. Thus even mild or subtle decline in memory and executive functioning, albeit in the average range of performance, can affect the ability to successfully manage medications in PD. These data support the importance of neuropsychological screening and assessment, even in patients with little to no report of cognitive dysfunction.
Evidence of a relationship between cognitive test performance and instrumental activities of daily living (IADL) in PD is not novel. Recently, in non-demented adults with PD, Rosenthal et al. (2010)
found medium to large effects between brief cognitive screening measures and informant report of IADL functioning. Results revealed the magnitude of the relationship between the MMSE and IADL functioning (r
=.36) was significantly less than that of the DRS and IADL functioning (r
=.52). While we concur with the authors’ conclusion that sensitive cognitive assessments are needed to elucidate functionally relevant impairments in non-demented adults with PD, we believe the relationship between cognition and functioning in PD also benefits from sensitive performance-based functional assessment. Goldberg and colleagues (2010)
recently illustrated the benefits of performance-based assessment over informant IADL report in a sample of non-PD adults with MCI and cognitively healthy older adults. Goldberg et al.’s (2010)
findings revealed that adults with MCI demonstrated deficits on a performance-based measure of functional assessment even when they were described as free of any IADL deficits on traditional questionnaires. Our findings suggest the HMS is more sensitive to cognitive performance than self-reported ability of medication management. Further work is needed to examine if the HMS is more sensitive to subtle cognitive changes than traditional informant report of IADL difficulty.
There are limitations to the present study. Foremost, our sample size was comprised of only 26 patients with PD. Thus future work is needed to confirm the generalizability of our results. Second, we did not obtain potentially useful information on the comorbid medical conditions of our participants, nor did we record participants’ actual medications (although all participants were taking a regimen of dopaminergic therapy). Future work should also explore the role of comorbid illness (e.g., cardiovascular disease) on medication management in PD. One might hypothesize that additional illnesses (and subsequent medications) may detrimentally affect medication management skills in PD. Third, 8 minutes was used as a cut-off for completion of both the standard HMS schedule and the modified PD schedule component. The 8-minute criterion was based on results from Carlson et al. (2005)
who found older women, on average, were able to complete the standard HMS schedule in 3.8 minutes. However, the use of the 8-minute cutoff might have inadvertently resulted in poor scores for participants who, when given additional time, would have been able to complete the HMS and PD schedules. We recommend future work allow more time for the completion of the HMS schedules, although an inability to complete the schedule in 8 minutes likely represents a significant deficit in most clinical groups to be studied. Finally, our work did not take into account compensatory strategies of medication management (e.g., assistance from a spouse). Future work would benefit from input from knowledgeable study partners. However, the groups of men who successfully completed the total schedule and pillbox did not differ in reported difficulty with self-medication management. Therefore, overall, we conclude the HMS, and the PD-specific modified components may prove a brief and useful measure of the ability to successfully manage medications in older adults with PD with mild cognitive difficulties.
In summary, the ability to manage one’s medications is a complex task involving a number of core neuropsychological and motor skills. The present findings suggest working memory, verbal learning and recall, and cognitive flexibility are especially important to successful medication management as measured by the HMS. Whereas the reasons for medication noncompliance in the PD are likely multifactorial, it is concerning that such a large percentage of patients appear unable to self-manage medications, given this is so important for optimal management of symptoms. A potential hypothesis is that deficits would be even more apparent if prospective memory was involved; that is, if the PD patient must self-remember a dose time, know which medications to take at that time, and to actually take the medication as prescribed. The routine use of structured questionnaires such as the HMS along with a good screening battery of neuropsychological measures can help identify any cognitive and motoric barriers in a given patient and aid in the development of specific compensatory strategies or implementation of remediation techniques. Potential interventions worthy of future study include pharmacist-patient counseling and education focusing on the importance of individual medications and the use of schedules, timers, or other techniques aimed at increasing compliance.