Final answer:
To distinguish Otitis Externa (OE) from a ruptured Acute Otitis Media (AOM), the presence of tenderness with movement of the pinna is the most helpful clinical finding, as it suggests OE, also known as swimmer's ear.
Step-by-step explanation:
The most helpful clinical finding to distinguish Otitis Externa (OE) from a ruptured Acute Otitis Media (AOM) is A) Tenderness with movement of the pinna. Otitis Externa, or 'swimmer's ear', includes symptoms such as itching, redness, discomfort of ear canal, progressing to fever and pain which are exacerbated by touching or moving the external parts of the ear, including the pinna. It is often caused by bacteria, like Pseudomonas aeruginosa. On the other hand, AOM involves the middle ear and is characterized by pus accumulation leading to severe bulging of the tympanic membrane and pain, which may especially be noticed during swallowing, but the key distinguishing feature is tenderness when moving the pinna, which is not commonly observed with AOM.