This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ear, Subject name: ENT
Glycerol test is done in 
Select and explain. 
A. Otosclerosis, B. Lateral sinus thrombosis, C. Meniere's disease, D. None of the above
C: Meniere's disease
Answer: C: Meniere's disease 
Explanation: Glycerol is a dehydrating agent. When given orally, it reduces endolymph pressure and thus causes an improvement in hearing. It is diagnostic of Meniere's disease. The patient is given glycerol(1.5ml/kg) with an equal amount of water and a little flavouring agent or lemon juice. Audiogram and speech discrimination scores are recorded before and 1-2 hr after ingestion of glycerol. An improvement of 10db in two or more adjacent octaves or gain of 10 c/o in discrimination score makes the test positive. There is also improvement in tinnitus and in the sense of fullness in the ear. The test has a diagnostic and prognostic value. These days, the glycerol test is combined with electrocochleography. Ref: Diseases of EAR, NOSE and THROAT by PL Dhingra 7th Edition page no.113