## **Core Concept**
Achalasia is a motility disorder of the esophagus characterized by the failure of the lower esophageal sphincter (LES) to relax, leading to difficulty in swallowing. Manometric features are crucial for its diagnosis. The condition involves abnormal peristalsis and impaired LES relaxation.

## **Why the Correct Answer is Right**
The correct manometric features of achalasia include elevated LES resting pressure, incomplete or failure of LES relaxation, and aperistalsis (absence of peristalsis) in the esophageal body. These features are diagnostic and help differentiate achalasia from other esophageal motility disorders.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Elevated LES resting pressure is a feature of achalasia, making it incorrect as an "except" option.
- **Option B:** Failure of LES relaxation is a hallmark of achalasia, which is why it's not the correct answer to the "except" question.
- **Option C:** Aperistalsis or absence of normal peristalsis in the esophageal body is another characteristic feature, so it's not the correct "except" answer.
- **Option D:** Increased peristalsis is not a feature of achalasia; rather, achalasia is characterized by aperistalsis. This makes it stand out as different from the typical manometric features of achalasia.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that achalasia can be diagnosed with a combination of clinical presentation (dysphagia to both solids and liquids), barium swallow showing a "bird's beak" appearance, and manometric findings as mentioned. It's essential to remember that achalasia is a cause of pseudo-obstruction and that its manometric diagnosis helps in planning treatment, which may include pneumatic dilation or Heller myotomy.

## **Correct Answer:** D. Increased peristalsis.