Episode 3: Achalasia — Pathophysiology, Etiology, and DiagnosisEpisode keywords: achalasia pathophysiology, ganglion cell degeneration, achalasia subtypes, achalasia diagnosis, pseudoachalasia, Chagas disease esophagus, bird beak sign, achalasia manometry, Type I Type II Type III achalasiaEpisode SummaryAchalasia means "does not relax." The name is the disease. This episode builds from the tissue level — selective inhibitory neuron degeneration — through the HRM subtypes that predict treatment response, to the diagnostic pathway that catches malignancy before it is missed. Understanding the pathophysiology allows you to derive every clinical feature rather than memorize it.Key TopicsCore lesion: Degeneration of myenteric (Auerbach) plexus ganglion cells, with preferential loss of inhibitory (nitric oxide-producing) neurons. Cholinergic excitatory neurons are relatively spared, producing unopposed excitation — this is why basal LES pressure rises.Result: Aperistalsis in the esophageal body; incomplete LES relaxation due to lost inhibitory innervation. Neuronal damage can extend to the dorsal motor nucleus of the vagus and vagal fibers.Etiology: Autoimmune (HLA associations, viral triggers including HSV, measles, HPV); emerging Type 2 allergic inflammation hypothesis (eosinophil/mast cell accumulation with association to EoE).Chagas disease: Trypanosoma cruzi infection causes identical ganglion cell loss. Manometrically indistinguishable from primary achalasia. Mandatory serologies for patients from Central/South America.Pseudoachalasia: Malignancy at the EGJ (classically adenocarcinoma) can mimic achalasia by neural invasion or paraneoplastic mechanisms. Red flags: age >55, rapid progression (<1 year), significant weight loss, endoscopic resistance traversing the GEJ. EGD before treatment is mandatory.Diagnostic pathway: Chest X-ray (widened mediastinum, absent gastric bubble) → barium swallow (bird-beak sign, dilated or sigmoid esophagus) → endoscopy (retained material, LES traversable with gentle pressure) → HRM confirmation.The three subtypes:Type I: Inert body, no pressurization. Complete loss of excitatory and inhibitory neural function.Type II: Panesophageal pressurization ≥20% of swallows. Residual excitatory function. Best treatment response.Type III: Premature (spastic) contractions ≥20% of swallows, DCI >450, DL <4.5 sec. Worst treatment response.Board PearlsHigh-yield: Type II → best response. Type III → worst response. This is the most consistently tested point about achalasia subtypes.Board trap: The LES in achalasia traverses easily with gentle endoscopic pressure. If it does NOT pass — think pseudoachalasia, not achalasia.High-yield: Absent gastric air bubble on chest X-ray in a dysphagia patient = elevated IRP preventing swallowed air from reaching the stomach.

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