Nonmotor symptom complex of Parkinson's disease--an under-recognized entity.

Parkinson's disease (PD) is the second most common neurodegenerative disorder, after Alzheimer's disease. The cardinal clinical features of PD include asymmetric onset of bradykinesia, rigidity, and resting tremor. Most patients of idiopathic PD present with one or more of the cardinal motor features. Apart from these, various nonmotor symptoms (NMS) also occur in PD and constitute a major clinical challenge, as they are common, but often overshadowed by the dominance of motor symptoms. NMS can present at any stage of the disease including early and pre-motor phase of PD. Several NMS such as olfactory dysfunction, constipation, REM behaviour disorder, depression may antedate the motor signs, symptoms and diagnosis of PD by a number of years. Since, NMS add significantly to the overall disability caused by PD, their early recognition and treatment may go a long way in improving the quality of life of PD patients as well as the economic burden on the carers. The identification of NMS can be improved by the application of quantitative and validated instruments and scales for their assessment.