• Suspect Parkinson's disease if the person has any of the following characteristic features (which, early in the disease, are usually unilateral, but become bilateral as the disease progresses):
• Bradykinesia (slowness of movement) or hypokinesia (poverty of movement) — for example:
• Reduced facial expression, arm swing, or blinking.
• Difficulty with fine movements such as buttoning clothes and opening jars, or small, cramped handwriting.
• Slow, shuffling gait, or difficulty turning in bed.
• Stiffness or rigidity, which may be:
• Lead-pipe rigidity, which describes the constant resistance felt when a limb is passively flexed in the presence of increased tone without tremor, or
• Cogwheel rigidity, which describes the regular intermittent relaxation of tension felt when a limb is passively flexed in the presence of tremor and increased tone.
• Rest tremor, which:
• Usually improves on moving.
• May appear at the thumb and index finger ('pill-rolling'), the wrist, or the leg.
• Is absent in up to 30% of people at disease onset.
• The following non-motor symptoms may also be present early in the disease (and may precede motor symptoms):
• Depression, anxiety, and fatigue.
• Reduced smell.
• Cognitive impairment.
• Sleep disturbance.
• Constipation.
• The following features may also be present if the person presents later in the disease:
• Postural instability (such as tendency to fall backwards after a sharp pull from the examiner: the 'pull test'), postural (orthostatic) hypotension (blood pressure decreases on standing up), and falls.
• Dementia and psychosis.
• Dysphagia (difficulty swallowing).
• Parkinson's disease may be confused with other causes of tremor and parkinsonism (see Differential diagnosis and Differentiating Parkinson's disease from drug-induced parkinsonism).

These recommendations are based on a guideline produced by the National Institute for Health and Clinical Excellence (NICE), Parkinson's disease: national clinical guideline for diagnosis and management in primary and secondary care [National Collaborating Centre for Chronic Conditions, 2006].

• Examples of bradykinesia and hypokinesia all had statistically significant positive and negative likelihood ratios for a diagnosis of Parkinson's disease in a systematic review on the precision and accuracy of clinical features for diagnosing Parkinson's disease [Rao et al, 2003].
• Only six studies met the inclusion criteria; all six studies were small and had important methodological limitations (mainly selection bias).
• However, the disease features listed are generally accepted in the NICE full guideline [National Collaborating Centre for Chronic Conditions, 2006] and in published review articles [Frank et al, 2006; Jankovic, 2008].
• Additional early and later symptoms of Parkinson's disease are derived from the NICE guideline and from narrative reviews [Alves et al, 2008; Weintraub et al, 2008].
• The caution that up to 30% of people with Parkinson's disease do not have tremor at disease onset is derived from narrative reviews [Frank et al, 2006; Jankovic, 2008; Weintraub et al, 2008].