Symptomatology and Clinical Features of Parkinson's Disease

Introduction

Parkinson’s disease (PD) is the second most common neurodegenerative disease and the commonest movement disorder worldwide. Clinically, PD is characterised by its cardinal motor symptoms which are Akinesia/bradykinesia, muscular rigidity, postural instability and resting tremor. It is highly established that these motor symptoms are caused by the degeneration of the dopamine (DA) producing neurons of the substantia nigra pars compacta (SNpc) of the midbrain leading to the nigrostriatal pathway dysregulation (Surmeier, 2018; Desai et al., 2019 ; Gelders et al., 2018). It is believed that during the onset of these cardinal motor symptoms, around 80% of dopaminergic neurons are already degenerated (Chung et al., 2001). The current standard diagnosis of PD is clinical and the disease is usually diagnosed by the first motor symptoms.

The progression of symptoms in PD is highly variable among patients (Poewe, 2006). Indeed, one of the main issues in PD diagnosis is that every patient is different regarding the symptoms, severity, and progression; hence, it is even sometimes said that each patient has his or her own version of PD (Sveinbjornsdottir, 2016b). However, the presence of PD cardinal motor features is essential in order to differentiate PD from related parkinsonian disorders. Another important thing that can help to distinguish PD from the other parkinsonian syndrome is that most motor symptoms of PD are responsive to dopaminergic therapy and the main confirmation of PD identification is the positive response to dopaminergic therapy (D’costa et al., 1995; Váradi, 2020).

Although in recent decades there have been large advances in symptomatic therapy of PD, therapies that will halt or slow the progression of the disease remain challenging (Poewe and Mahlknecht, 2009). With the disease progression, other motors and non motor symptoms (NMS) appear either as a result of the disease course or as complications of these pharmacologic testaments which eventually worsen both PD diagnosis and management. The NMS of PD includes sleep disorders, neuropsychiatric dysfunction, sensory symptoms, cognitive impairment, and dementia among others are also associated with poor quality of life (Schapira etal., 2017; Ja et al., 2012; Ziemssen and Reichmann, 2007). Additionally, most if not all PD symptoms are progressive, and their management is of great importance. In this chapter, the critical features of PD and their utilization in the clinical diagnostics are discussed.