During which condition is the tympanic membrane (TM) most likely to bulge?

The tympanic membrane (TM) is most likely to bulge during suppurative otitis media. This condition is characterized by the accumulation of pus in the middle ear due to bacterial infection. As the infection progresses, the pressure from the fluid buildup behind the TM causes it to bulge outward.

In contrast, viral upper respiratory infections may cause mild fluid in the middle ear but typically do not result in significant pressure or bulging of the TM. Allergic rhinitis can lead to eustachian tube dysfunction and potentially fluid accumulation, but it generally does not cause the level of inflammation and pus associated with suppurative otitis media. Acute pharyngitis primarily affects the throat and does not directly cause changes to the TM. Therefore, the presence of pus and significant pressure in the middle ear during suppurative otitis media is what leads to the distinct bulging appearance of the tympanic membrane.