Currently, there is no specific test to definitely diagnose PD. The diagnosis is made by a neurologist following a thorough examination. An MRI of the brain may be ordered to exclude other brain diseases. However, there are no clear changes on the MRI that can conclusively tell that a person has PD. While not everyone will develop all four cardinal symptoms (slowness of movement or bradykinesia, tremor, rigidity or stiffness and loss of balance or postural instability), at least two are required for diagnosis, in the absence of an alternative cause (for example, exposure to certain medications or history of strokes). When symptoms first appear and signs are subtle, a precise diagnosis may be difficult.