Predictive value of nigrostriatal dysfunction in isolated tremor: a clinical and SPECT study

The overlap among tremor disorders is wide and complex because essential tremor patients may present resting tremor coexisting with postural tremor, while postural may coexist with resting tremor in Parkinson's disease. We investigated dopamine transporter binding in 61 subjects presenting with isolated atypical tremors defined as unilateral either postural, resting, or mixed (i.e. resting and postural) tremor, without rigidity or bradykinesia, by means of 123I-FPCIT SPECT imaging at baseline. Patients were followed-up clinically for 28.4 +/- 7.2 months. Twenty-five patients with baseline normal SPECT continued to present only tremor at follow-up. Among 36 patients with abnormal SPECT, 23 (64%) developed PD, while the remaining 13 continued to present only tremor at follow-up. The value of 123I-FPCIT SPECT in predicting the evolution to PD was very high in a way independent from the first clinical presentation of tremor (Rest tremor, P = 0.015; Mixed tremor, P = 0.015; Postural tremor, P = 0.039; chi-square test). Our data suggest that the clinical presentation of isolated tremors is insufficient to allow a precise early-stage diagnosis, whereas the detection of presynaptic nigrostriatal dopaminergic dysfunction could lead to diagnosis of atypical tremor disorders at a very early stage. We suggest this disorder to be labeled as "isolated tremor with dopaminergic presynaptic dysfunction".