Dysdiadochokinesia

Dysdiadochokinesia, dysdiadochokinesis, dysdiadokokinesia, dysdiadokokinesis, or DDK (from Greek dys "bad", dia "across", docho "receive", kinesia "movement") is the medical term for an inability to perform rapid, alternating movements.

Causes
It is a feature of cerebellar ataxia, and is the result of lesions to the posterior lobe of the cerebellum. It is thought to be caused by the inability to switch on and switch off antagonising muscle groups.

Dysdiadochokinesia is also seen in Friedreich's Ataxia and multiple sclerosis, as a cerebellar symptom (including ataxia, intentional tremor & dysarthria).

Presentation
It is commonly demonstrated by asking the patient to tap the palm of one hand with the fingers of the other, then rapidly turn over the fingers and tap the palm with the back of them, repeatedly. This movement is known as a pronation/supination test of the upper extremity. A simpler method using this same concept is to ask the patient to demonstrate the movement of trying a door knob or screwing in a lightbulb.

Another method of testing for this condition is called the heel to shin test. This is performed by having the patient in a supine or sitting position. The heel of one foot is rubbed up and down the shin of the opposite leg in a rapid movement. A positive sign of this condition would be that the patient was not able to perform this movement quickly or steadily, instead showing slow and wobbly movements.