Antiparkinsonian dopaminergic drugs increase the susceptibility to paranoid symptoms in many patients suffering from Parkinson's disease. Paranoid symptoms most often occur as visual, sometimes acoustical hallucinations. Abnormal tactile sensations and delusional infestation (DI) have only been described in a single case of Parkinson's disease treated with L-DOPA and amantadine but not with piribedil. Conversely, DI is often induced by illicit dopaminergic drugs. Apart from dysfunctional dopaminergic neurotransmission the pathophysiology of DI is poorly understood. A case of Parkinson's Disease with stable, but insufficient L-DOPA/decarboxylase inhibitor MAO-B-inhibitor treatment is described. The addition of piribedil led to marked DI, while previous additions of ropinirole and pramipexole had not. This is the first report of delusional infestation induced by piribedil add-on in Parkinson's disease and the second case of antiparkinsonian medication-induced DI in general. Piribedil's stronger antagonism at central alpha2-receptors, as compared to ropinirole and pramipexole, and the resulting increased cortico-limbic adrenergic neurotransmission and dopamine release best explain the formation of drug-induced DI in this case, carefully pointing to neural mechanisms beyond the dopamine system in this disorder.
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Kölle et al. (2010) studied this question.