Non-Motor Symptoms in Parkinson’s Disease

Parkinson’s disease encompasses a spectrum of motor and non-motor manifestations, with the latter often preceding motor symptoms and influencing disease trajectory. Sensory dysfunction, sleep-related disorders, autonomic impairment, neuropsychiatric symptoms, and cognitive decline reflect widespread neurodegeneration involving the brainstem, limbic system, and peripheral nervous system. Hyposmia and visual dysfunction are emerging as early biomarkers, while chronic pain and paraesthesias indicate central and peripheral nociceptive dysregulation. Sleep-related disorders, particularly REM sleep behaviour disorder and insomnia, frequently arise in the prodromal phase, highlighting disruptions in circadian regulation and neuroanatomical integrity. Neuropsychiatric symptoms—including depression, anxiety, apathy, and hallucinations—result from complex dysregulation of dopaminergic, serotonergic, and noradrenergic pathways, compounding disease burden and impairing quality of life. Autonomic dysfunction, affecting cardiovascular, gastrointestinal, thermoregulatory, and genitourinary systems, underscores the systemic nature of the disease. Despite growing recognition of these non-motor features, treatment strategies remain limited, constrained by a dopamine-centric therapeutic framework that does not fully address broader neurobiological dysfunction. The lack of reliable biomarkers hampers early diagnosis and precision medicine approaches, while the conventional dichotomy between motor and non-motor symptoms has hindered the development of integrative treatment paradigms. While previous reviews have examined individual non-motor manifestations in detail, this article provides a comprehensive synthesis, offering a clinically relevant perspective for medical students, primary care physicians, and non-specialists. Recognizing non-motor symptoms as core disease manifestations rather than secondary sequelae is essential to refine diagnostic criteria and develop targeted therapies. Parkinson’s disease is a complex, multisystem neurodegenerative disorder that necessitates a paradigm shift in research priorities and clinical management. A broader, integrative perspective is required to redefine how the disease is understood, taught, and treated, ensuring that motor and non-motor symptoms are addressed to improve patient outcomes.