We read with great interest a recent article by Morgante et al1 concerning the prevalence of psychosis associated with Parkinson disease. Psychotic symptoms, mainly visual hallucinations (VHs), occur in about one -third of patients, and thought to be a complication of antiparkinsonian treatment. However, they reported that psychotic type symptoms of PD, such as VHs, might occur more frequently in the early stage compared with later stages. In population-based, case-control study, PD patients historical records were examined for depression and anxiety in pre-motor phase of PD.2-4 Notably, Shiba et al3 described that the association with anxiety was significant even when the analysis went as far back as 20 years before the onset of motor symptoms.3 These studies show that anxiety and depression are associated with PD and suggest that the causative process or risk factors underlying PD may be present many years before motor symptoms onset. Neither the mechanism of VHs nor frequency of VHs in pre-motor phase are not clear in PD. One potential explanation for VHs is the imbalance with cholinergic neurotransmission rather than dopaminergic overactivity due to antiparkinsonian treatment. Loss of dopaminergic nigrostriatal function occurs before motor symptoms onset in PD and influences the serotonergic, noradrenergic and cholinergic systems. We suspect that imbalance of cholinergic system induces the VHs in the early motor stage of PD. The beneficial effect of cholinesterase inhibitor on VHs supports our suggestion.5

REFERENCES 1. Morgante L, Colosimo C, Antonini A, et al. Psychosis associated to Parkinson's disease in the early stages: relevance of cognitive decline and depression. J Neurol Neurosurg Psychiatry 2012;83:76-82. 2. Alonso A, Rodriguez LA, Logroscino G, et al. Use of antidepressants and the risk of Parkinson's disease: a prospective study. J Neurol Neurosurg Psychiatry 2009;80:671-4. 3. Shiba M, Bower JH, Maraganore DM, et al. Anxiety disorders and depressive disorders preceding Parkinson's disease: a case-control study. Mov Disord 2000;15:669-77. 4. Weisskoph MG, Chen H, Schwarzschild MA, et al. Prospective study of phobic anxiety and risk of Parkinson's disease. Mov Disord 2003;18:646-51. 5. Kurita A, Ochiai Y, Kono Y, et al. The beneficial effect of donepezil on visual hallucinations in three patients with Parkinson's disease. J Geriatr Psychiatry Neurol 2003;16:184-8.

Conflict of Interest:

None declared