Diffuse Esophageal Spasm Corkscrew Esophagus

A 52-year-old woman presents with a 6-month history of intermittent dysphagia to both solids and liquids, accompanied by retrosternal chest pain that prompted cardiac workup (ECG and troponin normal). Upper endoscopy was unremarkable. A barium esophagram shows the appearance marked **A** in the diagram—a tortuous, corkscrew-like esophageal lumen with multiple simultaneous segmental contractions. High-resolution esophageal manometry confirms normal lower esophageal sphincter relaxation (IRP 12 mmHg) with ≥20% premature distal contractions (distal latency 3.8 seconds). Which of the following best explains the underlying pathophysiology of the disorder demonstrated by structure **A**?