What clinical finding is pathognomonic for malignant otitis externa?

Malignant otitis externa is a severe infection that typically occurs in immunocompromised individuals and is often caused by Pseudomonas aeruginosa. One of the hallmark features of malignant otitis externa is the presence of granulation tissue at the floor of the bone-cartilage junction in the external auditory canal. This finding is significant because it indicates the invasive nature of the infection, as it involves not just the soft tissue but also the underlying bone.

The presence of granulation tissue signifies a chronic infection process, often reflecting an ongoing inflammatory response characterized by the formation of new connective tissue in the affected area. This tissue can serve as a nidus for further infection and complicate treatment.

Other clinical findings such as purulent drainage and ear pain are common in various forms of otitis externa but are not specific to the malignant form of the disease. An intact tympanic membrane may also be seen in cases of malignant otitis externa, and ear pain when touching the tragus indicates outer ear involvement but does not provide the specificity needed to diagnose malignant otitis externa. Hence, the emergence of granulation tissue at the bone-cartilage junction is a defining pathological feature that distinguishes malignant otitis externa from other ear infections.