What causes pencil thin stools?

Pencil thin stools can be caused by a narrowing in the colon, rectum or anus, or may occur as a result of diarrhea.

Causes of pencil thin stools related to narrowing of the colon, rectum or anus

Causes of colonic or anorectal narrowing include:

  • Anal cancer
  • Anorectal stenosis (narrowing of the anus or rectum, which can be due to scarring from inflammatory conditions, fissures, ulcers, trauma, or surgery)
  • Colorectal cancer
  • Polyps in the colon

Diarrhea-related causes of pencil thin stools

Pencil thin stools can also be due to conditions that cause diarrhea including:

  • Bacterial, parasitic or viral infection of the gastrointestinal tract
  • Diverticulitis (inflammation of an abnormal pocket in the colon)
  • Fecal impaction (hard stool that is difficult to pass)
  • Inflammatory bowel disease (including Crohn’s disease and ulcerative colitis)
  • Irritable bowel syndrome (IBS; digestive discomfort that does not cause intestinal damage or serious disease)

Serious or life-threatening causes of pencil thin stools

In some cases, pencil thin stools may be a symptom of a serious or life-threatening condition that should be immediately evaluated in an emergency setting. These include:

  • Bowel obstruction
  • Colonic volvulus (twisting of the colon)
  • Intussusception (telescoping of the intestines into themselves, which can reduce blood supply, cause obstruction, and tissue death)

Questions for diagnosing the cause of pencil thin stools

To diagnose your condition, your doctor or licensed health care practitioner will ask you several questions related to your pencil thin stools including:

  • When did you first notice pencil thin stools?
  • Have you noticed any other changes in your stool or bowel habits?
  • Are you having pain or discomfort anywhere?
  • Do you have any other symptoms?
  • Have you experienced any anorectal trauma or had anorectal surgery?
  • Have you had these symptoms before?
  • Do you have a family history of colorectal or other types of cancer?
  • What medications are you taking?

What are the potential complications of pencil thin stools?

Because pencil thin stools can be due to serious diseases, failure to seek treatment can result in serious complications and permanent damage. Once the underlying cause is diagnosed, it is important for you to follow the treatment plan that you and your health care professional design specifically for you to reduce the risk of potential complications including:

  • Anemia (low red blood cell count)
  • Bowel obstruction, perforation or infarction (severe injury to an area of the bowel due to decreased blood supply)
  • Dehydration and electrolyte imbalance due to long-term diarrhea
  • Poor nutrition due to vomiting, diarrhea, or a decreased desire to eat
  • Peritonitis (infection of the lining that surrounds the abdomen)
  • Spread of cancer
  • Spread of infection
  • Surgery to remove parts of the digestive tract due to obstruction, rupture, serious infection, or malignant condition


  1. Colon cancer. PubMed Health, a service of the NLM from the NIH. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001308/.
  2. Colorectal (colon) cancer. Centers for Disease Control and Prevention. http://www.cdc.gov/cancer/colorectal/.

What are pencil thin stools?

Changes in the stool can be related to changes in the diet or may be indications of a condition of the digestive tract. Narrowing of the stool may be due to a mass in the colon or rectum that limits the size of the stool that can pass through it. Conditions that cause diarrhea can also cause pencil thin stools.

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What other symptoms might occur with pencil thin stools?

Pencil thin stools may accompany other symptoms, which vary depending on the underlying disease, disorder or condition. Conditions that affect the digestive tract may also involve other body systems.

Digestive tract symptoms that may occur along with pencil thin stools

Pencil thin stools may accompany other symptoms affecting the digestive system including:

... Read more about pencil thin stoolssymptoms

Medical Reviewer: Cynthia Haines, MD Last Annual Review Date: Aug 7, 2013 Copyright: © Copyright 2014 Health Grades, Inc. All rights reserved. May not be reproduced or reprinted without permission from Health Grades, Inc. Use of this information is governed by the HealthGrades User Agreement.

This Article is Filed Under: Digestive System

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