Parkinson's: a syndrome rather than a disease?

Biomarkers of Parkinson's Disease: An Introduction

The development of biomarkers is of great importance in Parkinson's disease (PD) as it may contribute to confirmation and support of the diagnosis, tracking of progression, and prediction of the natural history of PD. Biomarkers also help in the identification of targets for treatment and measuring the efficacy of interventions. Biomarkers are, therefore, crucial to understanding the pathophysiology of PD, the second commonest neurodegenerative disorder in the world. Modern understanding of PD suggests that it is a multipeptide, multiorgan disorder presenting with a heterogeneous clinical condition, both motor and nonmotor. Biomarkers need to reflect this neuropathological and clinical heterogeneity of PD. In this review, we outline some key advances in the field of clinical, genetic, neuroimaging, and tissue-based biomarkers proposed or used for PD. The individual sections will be covered in relevant chapters and our review is largely a primer aimed to alert readers to the current state of the various biomarkers proposed for PD. In doing so, we have also underlined the important role multimodal rather than single biomarkers could play in our future understanding of PD.

The Nonmotor Features of Parkinson's Disease

Nonmotor symptoms (NMS) of Parkinson's disease (PD) were recognized by the great James Parkinson himself who mentioned symptoms such as sleep dysfunction, delirium, dementia, and dysautonomia, in his seminal 1817 essay, "An Essay on the Shaking Palsy" (Parkinson, 1817). In spite of the key impact of PD NMS on quality of life, there was little holistic research and awareness till the validation and use of comprehensive tools such as the NMS questionnaire, scale, and the revised version of the unified PD rating scale. Research studies using these tools highlighted the key impact of the burden of NMS on quality of life of PD patients and the need for NMS to be routinely assessed in clinic. We now define PD as a motor and nonmotor disorder, and the natural history includes a long prodromal phase of PD dominated by a range of NMS. The prodromal phase is the subject of much research particularly in relation to neuroprotection and identifying subjects at risk. Use of NMS tools has also validated burden grading of NMS with cutoff values, which can be used as outcome measure in clinical trials. Finally, the complex multineurotransmitter dysfunction that is seen in PD has been shown to manifest clinically as nonmotor subtypes. Recognition of such subtypes is likely to lead to the emergence of personalized and precision medicine in PD.

Palliative Care for Patients and Families With Parkinson's Disease

Parkinson's disease is the second most common neurodegenerative disease worldwide. There is widespread consensus that Parkinson patients, their carers, and clinicians involved in their care would benefit from a fully integrated, need-based provision of palliative care. However, the concept of palliative care in Parkinson's disease is still poorly defined and, consequently, poorly implemented into daily clinical practice. A particular challenge is the gradually progressive nature of Parkinson's disease-with insidiously increasing disability-making it challenging to clearly define the onset of palliative care needs for Parkinson patients. As people with Parkinson's disease are now living longer than in the past, future research needs to develop a more robust evidence-based approach to clarify the disease events associated with increased palliative care needs, and to examine these, prospectively, in an integrated palliative care service. The modern palliative care outlook, termed "simultaneous care,",is no longer restricted to the final stage of disease. It involves incorporating a continuity of care, effective management of the chronic-palliative interface, and a multidisciplinary network of professionals working both in the community and in specialized clinics, with active involvement of caregivers. Although promising, there is still a need to demonstrate the effectiveness of palliative care for patients with Parkinson's disease.