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Gastro Exam

Assessing Anal Sphincter Tone

October 29th, 2020


  • How to Assess

  • Use the palpating finger to assess the resting tone of the anus. Ask the patient to squeeze down against the finger.
The internal anal sphincter (IS, autonomic) is responsible for the majority of resting anal tone, while the external sphincter (ES, voluntary) is responsible for the act of squeezing.

Increased Anal Sphincter Tone

  • Feel For

  • Increased tone of the anal sphincter, with difficulty passing a finger through the anal canal.
  • Causes of Increased Anal Tone

  • Stress / anxiety (external sphincter) - mostly related to examination
  • Spasm (internal sphincter) - fissure in ano, haemorrhoids, proctalgia fugax

Reduced Anal Sphincter Tone

  • Feel For

  • Inability to squeeze the anal sphincter against a gloved finger.
  • Causes of Decreased Anal Tone

  • Cauda equina syndrome (internal & external sphincter) - spinal cord compression / trauma
  • Pudendal neuropathy (external sphincter) - obstetric trauma, multiple sclerosis, diabetes mellitus
  • Anal trauma (internal / external sphincter) - obstetric, idiopathic, other
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