This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: CNS, Subject name: Medicine
Which of the following tests shall not be useful for diagnosis of patients of Ocular M.Gravis? 
Select and explain. 
A. MRI Brain, B. Spirometry, C. Anti MUSK antibody titer, D. Ice pack test
B: Spirometry
Answer: B: Spirometry 
Explanation: Patients of ocular myasthenia gravis will have ocular symptoms in form of diplopia and ptosis. Hence CNS causes of oculomotor nerve compression must be ruled out using MRI head. Spirometry would not be useful as chest muscle weakness is a feature of generalised M. Gravis. Anti- MUSK antibody is found in cases of ocular MG. Ice pack test is a non- invasive test for diagnosis where application of ice pack to eyes reduces the ptosis and weakness.