**14. Gangrenous inflammation associated with uncontrolled diabetes mellitus**

As abovementioned repeatedly, diabetes mellitus predisposes gangrenous inflammation, particularly when the disease is poorly controlled. Here, three special disease situations as severe complications of diabetes mellitus are described.

#### **14.1 Malignant otitis externa**

The external ear canal guards against infection by producing a protective layer of cerumen that creates an acidic and lysozyme-rich environment. Malignant otitis externa is a type of life-threatening infection in the aged and poorly controlled

diabetic patients. Those immunocompromised patients who suffer from acquired immunodeficiency syndrome, undergo chemotherapy, and take immunosuppressant medications such as glucocorticoids may also be vulnerable to this serious disease [145–149]. Once infection becomes established in the external meatus of the susceptible patient, the bacteria invade the underlying structures of the soft tissue and destroy the temporal bone, and finally resulting in septicemia. Malignant otitis externa should be suspected if tenderness, erythema, and/or edema of the external ear and adjacent tissues are noted on physical examination. *Pseudomonas aeruginosa* is the inciting organism in the vast majority of cases. Features of biofilm infection by Gram-negative rods are characteristic. The biopsy histology is illustrated in **Figure 52**. Much less frequently it is caused by *Staphylococcus aureus* and group A βhemolytic *Streptococcus*. Fungal etiology is also known, and *Aspergillus* and *Candida* can be the causative microbes. When untreated, the mortality rate is around 50%.
