A clinical overview of non-motor symptoms in Parkinson's disease

Although Parkinson's disease (PD) is diagnosed on the basis of motor symptoms, including slowness of movement, tremor, rigidity and difficulties with balance and walking, now we are aware that non-motor symptoms are highly prevalent, since they can anticipate motor symptoms and can cause severe consequences. Several studies have shown that non-motor symptoms, such as depression, anxiety and apathy, psychosis (e.g., hallucinations, delusions), sleep disturbance and pain may have a greater adverse impact on quality of life and health economics compared with motor symptoms. Non-motor symptoms can be divided into four domains: neuropsychiatric (e.g., depression, anxiety, apathy, hallucinations, dementia), autonomic (e.g., constipation, orthostatic hypotension, urinary changes, sweating abnormalities), sleep (e.g., insomnia, sleep fragmentation, excessive daytime sleepiness, rapid eye movement, sleep behavioural disorder, restless leg syndrome), and sensory dysfunction (e.g., pain, olfactory dysfunction). This review addresses diagnosis and treatment of these disorders. The causative mechanisms remain complex, since they reflect the widespread brainstem and cortical pathology of PD, with involvement of several neurotransmitters, including dopamine (DA), serotonin, norepinephrine, and acetylcholine. The diagnosis is often challenging, especially for psychiatric disorders, and in particular affective disorders, because somatic features of psychopathology may overlap with the movement disorder itself. Treatments used are limited and psychiatric drugs may not be as effective as in general population. Evidence based medicine is quite poor and it still requires well-designed clinical studies.