Streptococcal throat infections and exacerbation of chronic plaque psoriasis: a prospective study.

BACKGROUND: Guttate psoriasis has a well-known association with streptococcal throat infections but the effects of these infections in patients with chronic psoriasis remains to be evaluated in a prospective study.
OBJECTIVES: To determine whether streptococcal throat infections are more common in and can cause exacerbation in patients with chronic psoriasis.
METHODS: Two hundred and eight patients with chronic plaque psoriasis and 116 unrelated age-matched household controls were followed for 1 year. At recruitment all patients were examined, their disease severity scored and throat swabs taken. Patients and corresponding controls were then re-examined and tested for streptococcal colonization whenever they reported sore throat or exacerbation of their psoriasis during the study period.
RESULTS: The psoriasis patients reported sore throat significantly more often than controls (61 of 208 vs. three of 116, P < 0.0001), and beta-haemolytic streptococci of Lancefield groups A, C and G (M protein-positive streptococci) were more often cultured from the patients than the controls (19 of 208 vs. one of 116, P = 0.003). A significant exacerbation of psoriasis (P = 0.004) was observed only if streptococci were isolated and the patients were assessed 4 days or later after the onset of sore throat. No difference was observed between groups A, C or G streptococci in this respect.
CONCLUSIONS: This study confirms anecdotal and retrospective reports that streptococcal throat infections can cause exacerbation of chronic plaque psoriasis. It is concluded that psoriasis patients should be encouraged to report sore throat to their physician and that early treatment of streptococcal throat infections might be beneficial in psoriasis. A controlled trial for assessing potential benefits of tonsillectomy in patients with severe psoriasis should also be considered.