The gold standard for the diagnosis of achalasia is manometry, however a word of caution; An important differential diagnosis of achalasia is pseudo-achalasia (or false achalasia). Here achalasia is mimiced by infiltration of the lower esophageal sphincter by tumour so that it cannot relax. Always remember that an appearance of achalasia on imaging may be due to pseudo-achalasia. 4
Upper gastrointestinal endoscopy may miss the diagnosis entirely. The endoscopist may notice retention of food and saliva in the esophagus. The esophagus may appear larger then normal. If there is a huge mega-oesophagus the endoscopist may become confused and mistake the lower esophageal sphincter for the pylorus. There may be some inflammation in the lower esophagus, this is due to stagnation of food and fluid in the lower esophagus. It is usually possible to slip the endoscope through the lower esophageal sphincter without undue difficulty.
A contrast examination of the esophagus may show a mega-esophagus with a bird's beak appearance of the lower esophagus. The height of the contrast colum standing above the lower esophageal sphincter indicates the resistance in the lower esophageal sphincter.
The manometric features of achalasia are;