The most frequent NMS in Chaudhuri's tested cohort of PD patients using the NMS-Q included nocturia (66.7%), urinary urgency (61%), constipation (46.7%), memory (43.9%), and sadness (44.7%) [3
]. Further, in the Chaudhuri and Martinez-Martin cohort, the most prevalent symptoms using the NMS-S included nocturia (59.5%), urinary urgency (53.6%), constipation (50.2%), depression (48.2%), insomnia (44.3%), and concentration (44%) [4
]. A comparison to our cohort of advanced (presurgical) PD patients reveals similar findings but different rank order. When using the NMS-Q, patients in our study reported gastrointestinal, sleep, and urinary symptoms, and when using the NMS-S, PD patients reported sleep, gastrointestinal, and mood symptoms most frequently. The reasons for the differences include different cohorts, different disease severities, and a different demographic population. Also this advanced PD patient population was screened for cognitive findings and excluded for severe mood disorders prior to DBS surgery, and this may have also accounted for some of the differences.
The frequency of NMS among advanced PD patients varied in our study depending on the type of instrument utilized. For example, the frequency of mood symptoms was among the top 3 in the NMS-S, but in the bottom 3 in the NMS-Q. This could be a reflection of the difference of emphasis between the scales. In the NMS-Q, there were 2 questions that made up the mood subset, while, in the NMS-S there were 7. Devoting more questions to a particular symptom may increase sensitivity of the instrument for identifying milder manifestations of difficulty. In another example, in the NMS-Q scale, the gastrointestinal subset was composed of 9 questions, while in the NMS-S scale, the gastrointestinal subset was composed of only 3 questions. Finally, another important difference is that NMS-Q is patient driven while the NMS-S is clinician driven. In the mood example, clinician interpretation of a patient's answer may impact reporting differently than self-reported information. Self-report for items such as sexual difficulties may be more likely to capture full disclosure than face-to-face reporting, within a clinician-administered scale. For these reasons, the NMS frequencies differ and are instrument driven if they are compared head to head as a screening tool. This methodology of this study simplifies the results of the NMS-S, which is designed to assess impact of the NMS rather than simply screening for its presence as in the NMS-Q.
The correlation of NMS between patients and caregivers was also variable depending on the instrument and the symptom subset. In general, there was higher overall correlation in identifying NMS between PD patients and caregivers using the NMS-Q than with NMS-S. The NMS-Q had 5 subsets where the correlation between patient and caregiver responses was greater than 0.50, while the NMS-S had only 3 reaching this level. The 3 subsets with the highest patient/caregiver correlation using NMS-Q were mood, sleep, and urinary symptoms, and this differed from the 3 subsets with the highest patient/caregiver correlation using NMS-S where cognition, mood, and sexual items emerged. Of these most correlated NMS, only mood was within the highest correlated symptoms when using both instruments. The lack of correlation using the other symptom subsets between the patients and their caregivers may have been due to the caregiver's ability to recognize but not accurately rank the severity of symptoms close to how patients would report them. The NMS-Q is useful to screen for the presence of nonmotor symptoms in Parkinson's patients but does not reveal the extent that these symptoms affect quality of life. The NMS-S on the other hand takes into consideration the factors of duration and severity of symptoms that are present and extent that it affects the quality of life, but the instrument is more complicated and correct completion may require a trained member of the clinic/research team and not by patients themselves. The NMS-S was not designed to be administered to caregivers, as they are less apt than patients to more fully understand both the severity and duration of NMS that patients experience, which explains why there is lower correlation between patient and caregiver scores using the NMS-S than NMS-Q.
There were several limitations to our study. The small sample size was the greatest limitation. Furthermore, the prevalence of mood symptoms in this cohort may not have been truly representative of the general advanced PD state since unstable psychiatric illness and neuropsychological issues were screened out as part of establishing DBS candidacy. The data do speak to how commonly NMS occurs and that there may be issues with clinicians recognizing these features especially when focusing on motor issues and, interestingly, may be variably identified depending on which scale or questionnaire they use. Clinicians providing care and especially those providing DBS should be aware of the instrument-dependent nature of their recognition of these issues. The NMS-Q had better correlation between patients' and caregivers' reported symptoms, while the NMS-S offers the additional dimension of addressing severity of symptoms that are identified.
In summary, while these 2 instruments have their weaknesses and differences in instrument properties, they have been used in previous epidemiological studies as a basis for determining frequencies. We realize that while our N is small and the population is indeed biased to the “surgical patient.” this may prevent us from determining the true prevalence of NMS in advanced PD and explains the difference in results between our cohort and prior results reported by Chaudhuri. Our emphasis was not as much on the accurate accounting of each NMS, but more that, when converting these scale responses to a simple “symptom is present” versus “symptom is absent,” the responses indeed varied even if the two instruments were administered by the same individuals (patient and caregivers); literally, one instrument right after the other.