Enhancing the diagnostic potential of electroretinography in Parkinson's disease: A review of protocol and cohort criteria.

Degenerative parkinsonism in the Caribbean has shown distinct phenotypic and anatomopathological features, with a notable predominance of atypical parkinsonian syndromes over typical Parkinson's disease (PD). In the French West Indies (FWI), specifically in Guadeloupe and Martinique, most parkinsonian syndromes are atypical, accounting for 66–74% of cases. Only about one-third of patients meet the diagnostic criteria for PD, a stark contrast to other studies where atypical parkinsonian syndromes are reported at lower proportions (3–35%). Classically, atypical parkinsonian syndromes include four main disorders: progressive supranuclear palsy (PSP), multiple system atrophy, corticobasal degeneration, and dementia with Lewy bodies. These syndromes are characterized by poor or absent response to dopaminergic therapy, worse prognosis, and neurological “red flags” such as cognitive impairment or postural instability, that are rarely observed in PD at earlier stages of the disease, but quite frequent at advanced stages of PD. In the FWI, atypical parkinsonism, known as “Caribbean Parkinsonism” or “Caribbean Atypical Parkinsonism”, combines clinical features of various atypical parkinsonian syndromes subtypes. This nosological entity is endemic in both Guadeloupe and Martinique. It is characterized by a parkinsonian syndrome associated with a variable combination of additional signs such as supranuclear oculomotor palsy, cognitive decline, hallucinations, rapid eye movement sleep behavior disorder (RBD), dysautonomia, and myoclonus, sometimes combined in the same patient. Approximately half of Caribbean Atypical Parkinsonism cases resemble PSP, commonly termed PSP-like. Pathologically, Caribbean Atypical Parkinsonism is classified as a tauopathy based on limited pathological data but exhibits features characteristic of synucleinopathies rather suggesting mixed neuropathological lesions. Environmental origins have been linked to chronic exposure to toxins from plants used in traditional teas. Annonacin, a mitochondrial toxin found in these plants, has demonstrated neurotoxicity in both cell cultures and animal models. Chronic consumption of derivatives, leading to PSP-like syndromes, has been reported in regions where acetogenin-containing fruits are consumed. Given the socio-cultural and pharmacopoeial ties between the FWI (including Guadeloupe and Martinique), and French Guiana (often termed French Amazonia), both overseas French territories respectively in the Caribbean and in South America, we hypothesized that a similar degenerative parkinsonism profile might be present in French Guiana and that its links to environmental risk factors could be comparable. However, French Guiana has geographical, demographic, and cultural differences with the FWI, and this hypothesis, although plausible, has yet to be tested in the Guianese population. Indeed, French Guiana is a French overseas territory located on the South American continent, between Brazil and Suriname. This territory has the highest gross national product per capita in Latin American, which attracts many immigrants. As a result of these migratory flows, 29% of the population and nearly half of the adults are of foreign origin, primarily from surrounding South American countries. The population is mainly composed of French Guianese Creoles, continental French and Haitian Creoles, most of whom reside in coastal regions. The communes in the interior of French Guiana—mostly surrounded by Amazonian Forest—are inaccessible by road. The populations residing there are essentially Amerindians or Maroons. French Guiana is also home to other communities including those of Southeast Asian descent, contributing to its ethnic diversity. In French West Indies, the majority of the population consists of individuals of mixed African and European ancestry, followed by continental French. Other ethnic groups such as Asians (including Tamil, East Indians and Chinese communities) are less represented. French Guiana has a modern French universal health care system with a hybrid model combining public and private healthcare services, which is, by far, the highest health expenditure per capita in Latin America. In this context, the main aim of this study was thus to compare the prevalence of atypical parkinsonism between French Guiana and the FWI. Secondary objectives included describing the clinical features of atypical parkinsonian syndromes in French Guiana and assessing exposure to environmental toxins potentially linked to degenerative parkinsonism in patients from both regions.