Letter to the Editor
Congratulations on the concise article on anal fissure.1 It covered pathology and management well with one exception, the role of stool softening.
While the cause of an anal fissure is unknown, the condition is perpetuated by the cycle:
pain → internal sphincter spasm → faecal retention → hard stool → rapid anal stretching at (inevitable) defaecation → opening of the fissure → pain
This cycle can be broken by adequate stool softening. Increasing fibre intake is slow to act and often fails to give adequate softening. The stool needs to be as soft as toothpaste.
Osmotic agents (e.g. macrogol) or non-absorbed sugars (e.g. lactulose) can be used but have their disadvantages. The cheapest, most rapid acting product is liquid paraffin. A large dose can be given initially so that within 24 hours defaecation is pain free or almost so. In children, depending on their age, a dose of 20–30 mL to start can be followed by 10–15 mL twice daily. The dose can be easily adjusted according to the response. Liquid paraffin can be continued for two to three months, after which it is reduced slowly. Fibre can then be used if hard stools are a long-term problem.
As paraffin is not digested, does not change intestinal movement, and does not cause movement of water in or out of the gut, it is relatively safe. Some leaking of oil is seen occasionally but this can be controlled by lowering the dose by a few mL.
I have yet to find good evidence of a complication other than pulmonary aspiration secondary to gastro-oesophageal reflux. It is best to avoid giving a dose last thing at night. Macrophages in intestinal nodes can show micro droplets but no ill effect has been noted. About 30 years ago there was a belief that liquid paraffin could cause fat soluble vitamin deficiency, however this has not been substantiated by subsequent research.2Hugh Martin