Parkinson’s disease (PD) has traditionally been considered a motor system disorder, but it is now widely recognized to be a complex one with diverse clinical features that include neuropsychiatric manifestations [1]. Psychiatric features of PD include but are not limited to cognitive impairment, psychosis, anxiety, depression, apathy, sleep disturbances, as well as fatigue. In a multicenter survey of over 1000 patients with PD, virtually all (97%) of patients reported nonmotor symptoms, with each patient experiencing an average of approximately eight different ones [2].

Certain non-motor features of PD (e.g. olfactory dysfunction, constipation, depression, anxiety, and REM sleep behavior disorder) may even precede manifestation of motor symptoms [3, 4]. Psychiatric symptoms, especially psychosis and/or dementia, may be even more disabling than motor features [5, 6]

Non-motor symptoms (NMS) are important features in Parkinson’s disease (PD). Sleep disturbances have a high prevalence among NMS and affect quality of life of PD patients [1]. In this chapter we will describe the most important features of the main sleep disorders encountered in PD.

Monoamine oxidase (MAO), located in the outer mitochondrial membrane, is a critical enzyme in the metabolism of a number of neurotransmitters. Two isoforms of the enzyme exist, MAO-A and MAO-B [1]. These differ both in their tissue distribution and substrate selectivity. MAO-A is predominantly located in the periphery (including the gut) and preferentially catalyses the oxidation of 5-hydroxytyptamine (5-HT, serotonin) and norepinephrine [1]. MAO-B selectively metabolizes beta-phenylethylamine, while tyramine and dopamine are substrates for both types [1]. MAO inhibition, either non-specific or selective, increases the synaptic concentrations of the usually metabolized neurochemicals, providing symptomatic benefit in a variety of neurological and psychiatric disorders.

Value based healthcare is a key aspect of modern healthcare delivery. Outcome measures are therefore a major aspect of addressing the importance of healthcare delivery and the objectives it aims to achieve. Besides motor symptoms, non-motor symptoms (NMS) in Parkinson’s disease (PD) drive quality of life across all stages of the disease, as well as societal costs. Objective measurement is possible using validated tools, both patient self-rated and healthcare professional-administered. Mixed motor and non-motor objective assessments are therefore recommended in order to achieve an adequate evaluation and management tailored to the patients’ specific needs [1]. Furthermore, the availability of assessment instruments for detecting and measuring NMS has allowed understanding of their importance, progression, and impact on the patients’ daily life, and the estimation of the effect of interventions in PD patients [2].

People with Parkinson’s disease (PD) experience a variety of non-motor symptoms. Many of these non-motor symptoms can appear in the early phases, in still drug-naïve patients. Others tend to develop overtime, with prolonged disease duration and exposure to higher doses of dopaminergic therapy [1]. Often, non-motor symptoms fluctuate in response to levodopa similarly to the pattern observed in motor fluctuations [2]. Complex mechanisms underlie the development of PD non-motor symptoms, therefore, the term “drug-induced” used in this chapter does not mean to “blame” the therapy for such complications. Instead, as discussed along the chapter, in most cases, the antiparkinsonian therapy simply worsens or triggers specific non-motor symptoms because PD increases patients’ susceptibility [3].

Parkinson’s disease (PD) is an age-related neurodegenerative multisystem progressive disorder belonging to the α-synucleinopathy spectrum, with well-known and widely reported motor symptoms, such as tremor, rigidity, bradykinesia, and postural instability, and with highly prevalent and previously often neglected non-motor symptoms (NMS) [1], such as pain, depression, anxiety, sleep disturbances, cognitive dysfunction, and many others, that may precede the motor symptoms [2]. Sexual dysfunction (SD) is usually included in the category of autonomic NMS in PD, even though its etiology is multifactorial and involves interaction with other motor and NMS of PD [3–5]. Patients with PD rated SD twelfth out of 24 most bothersome symptoms of their disease [6], but SD remains an underrated non-motor feature of PD despite its high frequency and severe impact on the patient’s quality of life [7, 8].