By Eleanor McDermid
Data from a nationwide study show that people with the skin condition rosacea are at an increased risk of later developing Parkinson's disease (PD).
And the research also suggests that tetracycline - commonly used to treat moderate or severe rosacea - may have a protective effect against PD.
This is consistent with the effects noted for the similar drug minocycline hydrochloride in preclinical and early clinical trials and suggests the drug class should be further studied in PD patients, say Alexander Egeberg (University of Copenhagen, Denmark) and study co-authors.
Matrix metalloproteinases are upregulated in both rosacea and PD, and previous small studies identified high rates of rosacea or facial flushing in PD patients, prompting the researchers to initiate a large, population-based study. Their analysis included more than 5 million people, of whom 68,053 developed rosacea during up to 15 years of follow-up.
PD was subsequently diagnosed in 280 of these patients, giving an incidence rate of 7.62 per 10,000 person-years. This was nearly double the rate observed among people without rosacea (controls), of 3.54 per 10,000 person-years. Also, PD was diagnosed a significant average of 2.4 years earlier in rosacea patients than controls, at age 73.7 years versus 76.1 years.
Even after accounting for age, gender, socioeconomic status, smoking, alcohol abuse, comorbidity and medication, rosacea patients had a significantly increased incidence rate ratio of PD relative to controls, at 1.71. The increase was significant in both men and women, and persisted after adjusting for use of dopaminergic agents.
The risk of PD appeared to be similar regardless of the severity of rosacea - inferred from whether patients were prescribed topical metronidazole or oral tetracycline. However, in the whole cohort, patients who had used tetracycline had a small but significant 2% reduction in the risk of developing PD, leading the team to suggest that the higher risk of PD logically associated with more severe rosacea is counteracted by tetracycline use.
In an editorial accompanying the research in JAMA Neurology, Thomas Wingo (Emory University, Atlanta, Georgia, USA) observes that the link between rosacea and PD "may very well be true", but cautions that the finding needs to be replicated in an independent cohort before further research is justified.
But he also suggests that the "intriguing finding" of a "small but appreciable reduction" in PD risk associated with tetracycline should be explored further. "Of particular interest would be to understand the temporal association between the use of tetracycline and effect on PD risk", he says.
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