This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Salivary Glands, Subject name: Surgery
The 'Starch iodine test' is useful to diagnose: 
Select and explain. 
A. Wegener's granulomatosis, B. Cat scratch disease, C. Sarcoidosis, D. Frey's syndrome
D: Frey's syndrome
Answer: D: Frey's syndrome 
Explanation: The 'Starch iodine test' is useful to diagnose Frey's syndrome. This involves painting the affected area with iodine, which is allowed to dry before applying dry starch, which turns blue on exposure to iodine in the presence of sweat. Sweating is stimulated by salivary stimulation.