RESUMO
Internal anal sphincter achalasia (IASA) is a rare anorectal disorder that presents as chronic refractory constipation in pediatrics. With a poor response to conventional constipation-based therapy, it is often misdiagnosed as other conditions, such as ultra-short-segment Hirschsprung disease. This case report describes a rare case of IASA in an adolescent female, emphasizing the importance of ruling out other differentials, including Hirschsprung disease, via rectal biopsy and thus allowing for earlier targeted therapy to improve lifestyle conditions. A 20-year-old female with a history of IASA presents for semiannual botulism toxin injections. Despite initial relief, her constipation symptoms gradually returned after four to five months. She has had a history of ineffective conventional constipation treatments since childhood, which prompted a further workup. Biopsy results during her teenage years confirmed the presence of ganglionic cells, differentiating IASA from Hirschsprung disease. The management plan involved biannual perianal Botox injections, offering relief for approximately six months. IASA's physiological basis involves altered innervation, the absence of nitrergic nerves, and defective neuromuscular junctions in the internal anal sphincter. Diagnosis requires anorectal manometry and a rectal suction biopsy. Treatment options include botulism, toxin injections, and posterior internal anal sphincter myectomy. Botulism injections offer temporary relief, while myectomy provides long-term improvement.