[The apomorphine test in the differential diagnosis of Parkinsonism. Initial experience]

The reactivity of postsynaptic dopamine receptors in the striatum is preserved in Parkinson's disease (PD) but not in parkinsonian syndromes of various origin (PS). Hence, the effect of dopaminergic stimulation can serve as one of the diagnostic criteria allowing to distinguish between PD and PS. The present study aimed to ascertain the clinical utility of Apomorphine (APO), a powerful short acting direct D1 and D2 receptors agonist drug, in the differential diagnosis of PD and PS.

We studied 39 patients presenting parkinsonian signs. Based on clinical examination, 23 subjects (7 f, 16 m, mean age (SD) 59.2 (7.8) years were diagnosed as having probable PD, and 16 patients (5 f, 11 m, mean age 72 (7.6) yrs, p < 0.001) as having probable PS. In the PD group, mean Hoehn and Yahr degree of severity was 2.7 (1.1), mean duration of the disease 9.5 (6.2) yrs, mean duration of L-DOPA treatment (20 patients) 6.7 (5.5) yrs. In the PS group, the respective values of Hoehn and Yahr were 3.3 (0.9), mean duration of the disease 6.2 (4.1) yrs and mean duration of L-DOPA treatment (10 patients) 1.6 (1.1) yrs. After an overnight withdrawal of all other dopaminergic medication, a single subcutaneous dose of Apomorphine hydrochloride solution corresponding to 0.05 mg per kg of weight was administered. Domperidone was given 60 mg daily prior to the testing to avoid undesirable peripheral effects of APO. 20 minutes after APO administration, we noted a marked clinical improvement i.e. at least 30% decrease of pre-treatment motor score values on Columbina University Rating Scale (CURS) in 19 of 23 PD and in one of 16 PS patients. In the PD group, the difference between mean CURS values, 30.7 (19.5) before and 14.7 (10.3) after APO was highly significant (p < 0.001). In the PS group, only a slight posttreatment CURS decrease was found, 39.8 (17.5) before and 37.8 (17.5) after APO (p < 0.05).

In individual patients, these results mostly confirm the presumed diagnosis of PD or PS. Even in the most serious cases from the PD group, the testing showed that the function of dopamine receptors in the striatum was still preserved. Thus, the Apomorphine test appears to be a helpful tool for differential diagnosis of PD and PS.