This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Malabsorbtion Syndrome, Subject name: Medicine
Which investigation is not required in diagnosis of Achalasia? 
Select and explain. 
A. Esophageal manometry, B. Barium swallow, C. Anti-neuronal antibodies, D. Enterocylsis
D: Enterocylsis
Answer: D: Enterocylsis 
Explanation: Investigation Diagnosis CTchest Pseudoachalasia Endoscopic Ultrasound Pseudoachalasia Anti-neuronal antibodies Para neoplastic manifestation Enterocylsis Study small bowel using contrast study