Influenza Follicles.

A 28-year-old healthy man presented to our hospital with a 3-day history of a fever. Two days before his presentation, he had visited another primary care clinic, where his rapid influenza antigen test result had been negative. A physical examination revealed well-defined, round, shiny, magenta follicles on the posterior wall of the pharyngeal mucosa that resembled “salmon roe” (Picture A, white arrow). Smaller lymphoid follicle buds were not observed. We also conducted a rapid influenza antigen test that showed positive results for type B infection; thus, a diagnosis of influenza was established. Posterior pharyngeal wall follicles (called “influenza follicles”) were first reported in 2009 and are highly sensitive and specific for a diagnosis of seasonal influenza. The mechanism underlying the formation of these influenza follicles is suggested to involve rapid filling with lymph plasma-rich matrix and deposited fibrin (1). Therefore, if a physician observes influenza follicles during the period of influenza seasonal activity, it is likely to support a diagnosis of influenza. The patient's symptoms and follicles resolved after one week with conservative treatment (Picture B).

Picture.

The authors state that they have no Conflict of Interest (COI).