Pencil Thin Stools

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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.

Persistent pencil thin stool, which may be solid or loose, is one of the symptoms of colorectal polyps or cancer. As the size of the polyp or cancer increases, it can decrease the internal diameter of the colon or rectum so that only thin stool can pass through. Other symptoms can include blood in the stool, abdominal discomfort, and unintended weight loss, particularly in the case of advanced colorectal cancer. Colorectal cancers are diagnosed in about 140,000 people in the United States per year.

Narrowing of the rectum or anus can be caused by enlargement of the prostate in men or may be a complication of anal fissures (tears or cracks), rectal ulcers, Crohn’s disease or ulcerative colitis (inflammatory bowel diseases), or anorectal trauma or surgery.

The loosely formed stools of diarrhea may have a narrow, sometimes ribbon-like appearance. Diarrhea can have a variety of causes; it may go away on its own or become chronic. Diarrhea that is persistent or accompanied by other symptoms may require treatment.

Pencil thin stools that do not resolve within a couple of days or that are associated with other symptoms can be associated with serious conditions. Seek immediate medical care (call 911) if you have bloody stool, black or tarry stool, stool with pus, severe abdominal pain or cramping, high fever (higher than 101 degrees Fahrenheit), or if you suddenly stop passing stool. If you are having diarrhea, it increases your risk of dehydration, which can have significant complications. Symptoms of dehydration, such as decreased urination, excessive thirst, fatigue, and light-headedness, also require immediate medical care.

If your pencil thin stools are persistent or cause you concern, seek prompt medical care

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:

  • Abdominal pain or cramping

  • Abdominal swelling, distension or bloating

  • Abnormally foul-smelling stools

  • Bloody stool (blood may be red, black or tarry in texture)

  • Constipation

  • Diarrhea

  • Fecal incontinence (inability to control stools)

  • Gas

  • Mucus or undigested food in feces

  • Nausea with or without vomiting

  • Painful bowel movements

  • Urgent need to pass stool

Other symptoms that may occur along with pencil thin stools

Pencil thin stools may accompany symptoms related to other body systems including:

Serious symptoms that might indicate a life-threatening condition

In some cases, pencil thin stools may be a symptom of a life-threatening condition that should be immediately evaluated in an emergency setting. Seek immediate medical care (call 911) if you, or someone you are with, have any of these life-threatening symptoms including:

  • Bloody stool (blood may be red, black or tarry in texture)

  • Change in level of consciousness or alertness, such as passing out or unresponsiveness

  • Change in mental status or sudden behavior change, such as confusion, delirium, lethargy, hallucinations and delusions

  • High fever (higher than 101 degrees Fahrenheit)

  • Inability to pass stool

  • Not producing any urine, or an infant who does not produce the usual amount of wet diapers

  • Severe abdominal or rectal pain

  • Vomiting blood or rectal bleeding

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:

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

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Jan 6
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Colon cancer. PubMed Health, a service of the NLM from the NIH.
  2. Colorectal (colon) cancer. Centers for Disease Control and Prevention.