Treatment of Achalasia: Botulinum Toxin Injection vs. Pneumatic Balloon Dilation. A Prospective Study with Long-Term Follow-Up - Allescher , H D; Storr , M; Seige , M; Gonzales-Donoso , R; Ott , R; Born , P; Frimberger , E; Weigert , N; Stier , A; Kurjak , M; Rösch , T; Classen , M (Endoscopy, 2004)