Growth hormone response to low-dose apomorphine in restless legs syndrome

Low-dose apomorphine challenge has been shown to cause a rise in growth hormone (GH) in patients with Parkinson's disease (PD). This was interpreted as an increased postsynaptic sensitivity of hypothalamic dopamine receptors in the course of a generalized degeneration of dopaminergic neurons. The dopaminergic system in the restless legs syndrome (RLS) has been assumed to play a role in its pathophysiology. It is therefore the aim of this study to determine whether the GH response to subcutaneously applied low-dose apomorphine is generally altered in patients with RLS as compared to healthy controls.

We examined 40 patients with idiopathic RLS as well as 20 age- and sex-matched healthy control subjects by means of the low-dose apomorphine test. GH was analyzed at baseline, as well as 45 and 60 min after subcutaneous low-dose apomorphine injection in the morning.

Forty RLS patients (58.3+/-11.9 years, 32 females) with a mean RLS severity scale score of 23.9+/-6.6 (range 10-37) were examined. GH was not significantly increased 45 and 60 min after injection (p=0.397) (2.44+/-2.35 ng/ml at baseline versus 2.71+/-2.29 ng/ml after 45 min and 2.18+/-1.83 ng/ml after 60 min). The results were independent of pre-treatment with levodopa. Age, sex, duration, and severity of the disease did not show a covariate effect with GH levels. There was no difference compared with healthy controls.

RLS patients did not show an increase in GH after stimulation with low-dose apomorphine. Lack of sensitivity alteration of extrastriatal hypothalamic dopamine receptors suggests that RLS is not a general dopaminergic degenerative disease or might only show circadian alterations.