In which of the following conditions, uniform dilation of esophagus is seen -a) Sclerodermab) Achalasia cardiac) Dermatomyositisd) Trypanosoma cruzi infection

**Core Concept**
Uniform dilation of the esophagus is a characteristic feature of a specific motility disorder. This phenomenon occurs due to the failure of the lower esophageal sphincter (LES) to relax, leading to a buildup of pressure and subsequent dilation of the esophagus. The underlying pathophysiology involves a combination of impaired peristalsis and abnormal LES function.

**Why the Correct Answer is Right**
Achalasia is a primary esophageal motility disorder characterized by the failure of the LES to relax, leading to impaired esophageal emptying. This results in a uniform dilation of the esophagus, which can be visualized on barium swallow studies. The pathophysiology involves the degeneration of myenteric ganglia, leading to impaired peristalsis and a failure of the LES to relax. The absence of peristalsis and the failure of the LES to relax are the hallmark features of achalasia.

**Why Each Wrong Option is Incorrect**
* **Option A:** Scleroderma is a systemic autoimmune disease that can affect the esophagus, leading to fibrosis and decreased esophageal motility. However, it typically presents with a "rosary" or "corkscrew" appearance on barium swallow studies, rather than uniform dilation.
* **Option B:** Dermatomyositis is a systemic autoimmune disease that can affect the muscles and skin. While it can cause esophageal dysfunction, it does not typically cause uniform dilation of the esophagus.
* **Option D:** Trypanosoma cruzi infection, also known as Chagas disease, can cause megaoesophagus, which is characterized by a dilated and tortuous esophagus. However, this is typically seen in the chronic stage of the disease and is not uniform in nature.

**Clinical Pearl / High-Yield Fact**
Achalasia can be diagnosed using a combination of barium swallow studies, endoscopy, and manometry. The manometry study is particularly useful in diagnosing achalasia, as it can demonstrate the failure of the LES to relax and the absence of peristalsis in the esophagus.

**Correct Answer: C. Achalasia**