The potential role of Helicobacter species in the development of neuropsychiatric disorders has been a subject of interest, particularly in idiopathic parkinsonism (IP), where core motor symptoms can be objectively quantified. This systematic review, based on an EMBASE search, evaluated evidence addressing the association between Helicobacter infection and IP, the impact of bacterial eradication, and the outcomes of untreated infection, following Oxford Centre for Evidence-Based Medicine guidelines. Applying PRISMA criteria, 21 of 204 identified articles were included. Findings indicate that improvements following Helicobacter eradication are not solely due to enhanced levodopa absorption. A strong relationship exists between Helicobacter infection and IP, with H. pylori virulence factors—linked to autoimmune and immune tolerance mechanisms—affecting disease susceptibility, progression, and severity. The usual age-related pattern of virulence marker antibodies seen in healthy controls is absent in IP patients, supporting a causal role. Successful eradication in IP patients, including those naive to anti-parkinsonian therapy, appears to modify disease course but does not prevent onset. Motor symptoms such as hypokinesia improve, and overall motor impairment decreases. Nonetheless, eradication may alter gut microbiota in ways that potentially contribute to subsequent rigidity. Persistent H. pylori, even at molecular levels, or failed eradication, worsens hypokinesia. Short follow-up durations limit the assessment of long-term consequences of untreated infection. Overall, evidence supports Helicobacter as a significant pathophysiological contributor to IP.
