Differential Diagnosis for Pencil Shaped Stool

• Single Most Likely Diagnosis
  • Irritable Bowel Syndrome (IBS): Pencil-shaped stools are a common symptom in patients with IBS, particularly those with IBS-C (constipation-predominant). The narrow caliber of the stool is often due to the slow transit time through the colon, allowing for more water absorption.
• Other Likely Diagnoses
  • Lactose Intolerance or Other Carbohydrate Malabsorption: Conditions where the body cannot properly digest certain carbohydrates can lead to changes in stool shape and consistency, including pencil-shaped stools, due to the effects of undigested carbohydrates on bowel habits.
  • Inflammatory Bowel Disease (IBD): Both Crohn's disease and ulcerative colitis can cause changes in stool shape, including pencil-shaped stools, due to inflammation and narrowing of the bowel lumen.
  • Anal Fissure: Painful defecation due to an anal fissure can lead to spasm of the anal sphincter, resulting in narrow, pencil-shaped stools.
• Do Not Miss Diagnoses
  • Colorectal Cancer: Although less common, colorectal cancer can cause narrowing of the colon lumen, leading to pencil-shaped stools. This diagnosis is critical to rule out due to its severe implications.
  • Intussusception: A condition where a part of the intestine slides into an adjacent part, potentially causing bowel obstruction. It can lead to changes in stool shape, including pencil-shaped stools, and is a medical emergency.
• Rare Diagnoses
  • Hirschsprung's Disease: A congenital condition characterized by the absence of ganglion cells in the distal bowel, leading to severe constipation and potentially pencil-shaped stools, especially in children.
  • Chronic Intestinal Pseudo-obstruction: A rare condition where there are symptoms of bowel obstruction without any physical blockage, which can lead to alterations in stool shape and consistency, including pencil-shaped stools.