• Parkinson's disease
• essential tremor
• acute dopaminergic challenge test
• L-dopa

In Parkinson's disease, a postural/kinetic tremor may occur in association with the classical resting tremor. According to the consensus statement of the Movement Disorder Society on tremor,¹ this association is classified as type I (classical parkinsonian tremor) if the difference between the frequencies of postural/kinetic tremor and resting tremor is less than 1.5 Hz; and as type II if this difference is more than 1.5 Hz. In type I tremor, resting tremor and postural tremor share common pharmacological properties, responding to levodopa.^2,3 Type II tremor (that is, a predominant postural/kinetic tremor associated with a resting tremor of a lower frequency) is considered to be a combination of essential tremor and parkinsonian tremor, and is reported in between 3% and 24% of the patients diagnosed as having Parkinson’s disease.³ Though postural/kinetic tremor and resting tremor may show some overlap in their electrophysiological properties in Parkinson’s disease, the postural/kinetic component does not respond to levodopa.³ Nevertheless, clinical criteria may be insufficient to differentiate between Parkinson’s disease and essential tremor.

We report a case of a 70 year old patient affected by essential tremor and Parkinson's disease, in whom acute dopaminergic challenge tests allowed us to differentiate between the two components of severe bilateral arm tremor.

Acute dopaminergic challenge tests, which are well accepted as a diagnostic tool in Parkinson’s disease, may be helpful in …