The comorbidity and co-medication profile of patients with progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a rare neurodegenerative movement disorder with a mean onset between 60 and 66 years of age [1, 2]. Hence, PSP is a disease of elderly people, who often suffer from various additional chronic diseases. A previous report detected diabetes mellitus and cerebrovascular diseases as characteristic pre-diagnostic accompanying disorders of PSP.[3] A similar pattern of comorbidities in PSP, including arterial hypertension, was found in two other cohorts from Western countries [4, 5].

Treatment of the diverse motor and non-motor symptoms of PSP often requires the administration of multiple drugs [6, 7]. Together with the drug therapy necessary for comorbidities, this can result in polypharmacy [8]. The amount of administered drugs and therefore the prevalence of polypharmacy increases dramatically with patients’ age up to > 40% in people aged 85 years or older [9, 10]. Polypharmacy is a leading cause for drug-related problems, e.g., adverse drug reactions (ADR) or drug–drug interactions (DDIs), that may result in falls, hospitalizations or death [11‐13].

Since patients with PSP represent a highly vulnerable group, multimorbidity and polypharmacy should be given special attention in medical care. There currently is a lack of detailed knowledge on comorbidities and specific aspects of drug therapy in patients with PSP. In this study, we aimed to analyze the comorbidity profile and particular issues of drug therapy in PSP patients from two large German, multicenter PSP cohorts compared to a German, multicenter cohort of patients without neurodegenerative diseases. In addition, we elaborated aspects of drug safety in PSP patients with different disease phenotypes.

To our knowledge, this is the first systematic analysis of common comorbidities and relevant aspects of drug therapy in a large cohort of PSP patients compared to a multicenter cohort of patients without neurodegenerative diseases. PSP patients presented a specific profile of comorbidities, especially a considerably higher prevalence of cardiovascular and neurological diagnoses. In particular, diabetes mellitus, cerebrovascular diseases and polyneuropathies were found more frequently in PSP patients. Hence, more antithrombotic drugs and antidepressants were prescribed to PSP patients, but not cardiac or antidiabetic drugs.

So far, only few studies investigated the prevalence of cardiovascular diseases in PSP patients. The most reliable data in this regard are available for arterial hypertension. In two large cohorts of PSP patients from Germany and North America, the prevalence of arterial hypertension was 48% and 57%, respectively [4, 5]. Another study detected arterial hypertension in 50% of autopsy-confirmed PSP cases [23]. These data reflect the prevalence of hypertension in our cohort (54.6%). Moreover, diabetes mellitus was more prevalent in our PSP cohort compared to non-ND patients. The current literature indicates a prevalence of approximately 15% in the age of 70–79, which is comparable to that of the PSP group (13.4%) [24]. Lastly, PSP patients showed a significantly higher prevalence of cerebrovascular diseases than non-ND patients. With approximately 9.6%, the demonstrated prevalence in PSP was comparable to the age-matched prevalence of ischemic stroke in Germany, but considerably lower than in PSP patients prior to diagnosis [3, 25]. However, the observed differences in the prevalence of cardiovascular diseases and diabetes between PSP and non-ND patients could be based on a lower prevalence of these diseases in the non-ND group compared to data from other Western countries [24‐26].

An association between cardiovascular diseases, diabetes and neurodegenerative diseases is broadly assumed [27, 28]. A recent review attempted to illustrate the role of certain risk factors in Parkinson’s disease (PD) and cardiovascular diseases [28]. Based on common factors that increase (diabetes mellitus, male sex) or decrease (physical activity, moderate coffee consumption, female sex) the risk for both PD and cardiovascular diseases, the authors hypothesized shared pathophysiological pathways involving metabolic and inflammatory processes [28]. Previous reports have also shown an association between cerebrovascular and certain neurodegenerative diseases [29, 30]. Beside neurodegenerative diseases directly caused by a stroke, atherosclerosis and small-vessel disease was frequently detected as copathology in PD, Alzheimer’s disease (AD) and even in PSP.[31‐33] Moreover, the emerging basic scientific and epidemiological evidence suggest a linkage between diabetes mellitus and neurodegenerative diseases [27, 34‐36]. A recent meta-analysis showed that patients with diabetes were not only at higher risk for developing PD, but disease progression was also accelerated [35, 37]. In addition, Uyar et al. demonstrated poorer cognitive functioning in patients with PD and comorbid diabetes [34]. In this group of PD patients with cognitive decline, higher levels of serum neurofilament light chain (NfL) were detected, indicative for increased neuronal damage. The latter results are consistent with previous reports [38, 39]. Kwasny et al. analyzed pre-diagnostic features of a subsequent PSP diagnose in general practice and demonstrated for the first time an association between diabetes mellitus and PSP.[3] Interestingly, the group of untreated diabetics was markedly larger in the analyzed PSP cohort (25/45, 55.6%) compared to the non-ND group (1/13, 7.7%). This difference could be overestimated due to the small number of diabetics in the non-ND group. On the other hand, possible preventive effects of antidiabetic drugs could be considered. A number of epidemiological studies have examined the effect of antidiabetic drugs on AD, but obtained controversial results [27, 40, 41].

However, whether there is an indirect association via a common predisposition or a direct causal relationship of cardiovascular diseases, diabetes and neurodegenerative diseases remains a subject of much debate. A possible causality between cardiovascular diseases, diabetes and tauopathies is best described for AD. Baglietto-Vargas and colleagues extensively discussed the impact of diabetes on various pathophysiological processes involved in AD [27]. The disease-specific hyperglycemia and insulin resistance could initiate signaling pathways that impair neuronal glucose metabolism and thus stimulate phosphorylation and cleavage of tau as a cornerstone of tau accumulation and tau-mediated neurodegeneration [42, 43]. Furthermore, the accumulation of tau and β-amyloid in AD can be accelerated in the context of cardio- and cerebrovascular diseases [44, 45]. Due to a reduced cerebral blood flow and resulting hypoxia-induced ischemia, cerebrovascular diseases can induce a dysfunction of blood–brain barrier and mitochondria, enabling the deposition of misfolded proteins [44, 46]. On the other hand, cerebrovascular diseases and tau pathology appear to have a reverse association [47]. In this context, Kapasi and colleagues described increased tissue damage caused by small-vessel pathologies in the presence of β-amyloid and tau neurofibrillary tangles [48]. In addition to these causal considerations, the idea of a common predisposition or rather cause of cardiovascular diseases, diabetes and neurodegenerative diseases appears reasonable, since all of these result from an accumulation of misfolded proteins, for example β-amyloid or islet amyloid polypeptide (IAPP) [49, 50]. According to several hypotheses about the formation of misfolded proteins, molecular chaperones seem to play a crucial role [50]. Chaperones are highly conserved proteins that are an integral part of the proteostasis network regulation by acting as monitors for protein folding [51]. In the course of aging, various pathophysiological processes facilitate chaperone dysfunction and thus promote a disruption of proteostasis balance in favor of the accumulation of misfolded proteins [49, 52, 53]. More evidence is urgently needed to definitively answer these questions.

In our analysis, PSP patients suffered from significantly more pDDIs than non-ND patients. Since polypharmacy correlates directly with the number of pDDIs, the detected difference could be due to the higher number of administered drugs in PSP patients [54]. As previously described, the complex therapy of parkinsonism and associated comorbidities can facilitate polypharmacy [55, 56]. The prevalence of moderate and severe interactions in PSP patients was lower compared to a cohort of geriatric PD patients but considerably higher than reported in other cohorts of elderly [11, 55, 57]. Not only the sheer number of administered drugs, but also especially certain drugs, e.g., amantadine, amitriptyline and domperidone, pose a risk for pDDIs. The named drugs were involved in 66.7% of the contraindicated combinations in our PSP cohort because of their QTc-prolonging effects and consequent risk for cardiac arrhythmia [58‐61]. Further, the most frequent severe interaction was between diuretics/NSAIDs/agents acting on the renin-angiotensin system. Known as “triple whammy,” this dangerous combination can cause acute kidney injury, especially at the start of treatment [62‐64]. Since PSP patients show a non-negligible burden of cardiovascular diseases, which can often require the use of such a drug combination, and PSP patients represents a vulnerable group due to their disease-specific symptoms (e.g., dysphagia), pDDIs should be evaluated both at the beginning of a new drug therapy and during follow-up [65‐67].

Admittedly, this systematic acquisition and analysis shows some limitations. Due to diseases-specific symptoms, such as early cognitive dysfunction, the collection of a detailed medical history can be prolonged, incomplete or not possible from patients themselves [16]. Therefore, the interviewer is sometimes dependent on questioning caregivers which may lead to loss of information but avoids anosognosia. This reporting bias between the groups was particularly noticeable for diseases long past or rather acute, for example appendicitis. Another level of this reporting bias presumably results from being diagnosed with a chronic neurological disease. Hereby, PSP patients regularly keep an appointment with a neurologist, which promotes the identification of new diagnoses (e.g., polyneuropathy). Another limitation concerns the reliability of the non-ND cohort. First of all, the non-ND group was only similar to the PSP patient in basic demographic parameters after selection for age. This could be caused by a selection bias, since usually patients without neurodegenerative diseases were selected for the non-ND cohort. These patients may tend to be generally healthier than other people in this age. However, this does not diminish the quality and validity of the data from PSP patients. In this way, these data provide important insights into prevalence of certain comorbidities in PSP patients with different phenotypes.

The magnitude and complexity of disease burden in the aging population is one of the major challenges in future medicine. The polypharmacy often used for drug treatment of elderly not only endangers the individual patient safety, but also places a burden on the healthcare system. For this reason, precise knowledge of typical comorbidities and pitfalls of drug therapy is crucial. In this study, we demonstrate for the first time the number and profile of comorbidities as well as key aspects of drug therapy in a large cohort of PSP patients. Due to the non-negligible number of comorbidities, in particular neurological and cardiovascular, a large proportion of PSP patients showed polypharmacy. The obtained insights can improve mindfulness and thus more drug safety in the treatment of PSP patients.

Moreover, the detected burden of cardio—and cerebrovascular diseases in PSP patients supports previous reports suggesting an association of cardiovascular diseases and neurodegenerative diseases. Further research may uncover the pathophysiological connection between the two disease spectra. Based on this, cardiovascular diseases could represent possible modifiable risk factors for the development of PSP.