Emerging role of psychosis in Parkinson's disease: From clinical relevance to molecular mechanisms

Clinical characteristics and treatment of psychosis in Parkinson's disease: A narrative review

Parkinson's disease (PD) is a chronic, progressive, neurodegenerative disorder whose clinical presentation consists of motor and non-motor signs and symptoms. Among the non-motor symptoms, psychosis can occur in the later stages of the disease. Psychosis in PD (PDP) is a common, complex, and significantly disabling disorder associated with poorer quality of life, accelerated cognitive decline, need for hospitalization or institutionalization, and mortality. Hallucinations are a significant symptom of PDP, sporadic at first but more frequent in the later course of the disease, and significantly disrupt daily activities. Appropriate and timely screening of psychotic manifestations is necessary for adequate therapeutic procedures. After the exclusion of comorbid conditions as a possible cause of psychosis, correction of antiparkinsonian therapy may be required, and if necessary, the introduction of antipsychotics. The latest therapeutic recommendations include the use of pimavanserin, if available, otherwise second-generation or atypical antipsychotics. Although PDP has long been recognized as a possible complication in the course of the disease, further clinical studies are needed to fully understand its etiopathogenesis and pathophysiological mechanisms.

Brief commentary: Under-recognition of underuse of clozapine in treating psychotic symptoms in Parkinson's disease

Clozapine is an important drug in the treatment of Parkinson's disease (PD). It has proven efficacy in treating PD psychosis without worsening motor function, as well as in treating tremor refractory to L-Dopa, yet it is severely underused in the United States. Unlike the situation of treatment resistant schizophrenia, this underuse is underrecognized.

Rethinking Clozapine: Lights and Shadows of a Revolutionary Drug

The current literature globally highlights the efficacy of Clozapine in several psychiatric disorders all over the world, with an FDA indication for reducing the risk of repeated suicidal behavior in patients with schizophrenia or schizoaffective disorder. A growing field of research is also stressing a possible broader beneficial effect of Clozapine in promoting neuroprotection and neurotrophism. However, this drug is linked to several life-threatening side effects, such as agranulocytosis, myocarditis and seizures, that limit its use in daily clinical practice. For this work, a search was performed on PubMed using the terms "Clozapine indications", "Clozapine adverse effects", "Clozapine regenerative effects", and "Clozapine neuroplasticity" with the aim of reviewing the scientific literature on Clozapine's treatment indications, adverse effects and potential regenerative role. The results confirmed the efficacy of clozapine in clinical practice, although limited by its adverse effects. It appears crucial to raise awareness among clinicians about the potential benefits of using Clozapine, as well educating medical personnel about its risks and the early identification of possible adverse effects and their management.

The mechanisms of perineuronal net abnormalities in contributing aging and neurological diseases

The perineuronal net (PNN) is a highly latticed extracellular matrix in the central nervous system, which is composed of hyaluronic acid, proteoglycan, hyaluronan and proteoglycan link protein (Hapln), and tenascin. PNN is predominantly distributed in GABAergic interneurons expressing Parvalbumin (PV) and plays a critical role in synaptic function, learning and memory, oxidative stress, and inflammation. In addition, PNN's structure and function are also modulated by a variety of factors, including protein tyrosine phosphatase σ (PTPσ), orthodenticle homeo-box 2 (Otx2), and erb-b2 receptor tyrosine kinase 4 (ErbB4). Glycosaminoglycan (GAG), a component of proteoglycan, also influences PNN through its sulfate mode. PNN undergoes abnormal changes during aging and in various neurological diseases, such as Alzheimer's disease, Parkinson's disease, schizophrenia, autism spectrum disorder, and multiple sclerosis. Nevertheless, there is limited report on the relationship between PNN and aging or age-related neurological diseases. This review elaborates on the mechanisms governing PNN regulation and summarizes how PNN abnormalities contribute to aging and neurological diseases, offering insights for potential treatments.