Milk soy protein intolerance (MSPI) is a relatively common food intolerance seen in infants. It is caused by the inability to properly digest the proteins found in milk and soy. The proteins cause the lining of the GI tract to get inflamed and damaged. When this happens, the stool starts to get mucous and blood in it, and the infant gets really fussy (they cry all the time because their gut hurts). The diagnosis also goes by the name of food protein-induced colitis (which just means inflammation of the intestines).
MSPI should not be confused with lactose intolerance. Lactose intolerance is caused by a deficiency in the enzyme that breaks down the lactose (a milk sugar). It is very rare for lactose to cause a problem in infants.
There is no specific test to diagnose MSPI. It is diagnosed by history, physical exam, and response treatment. As for treatment, there is no specific medication. The treatment is an elimination diet. If the baby is breastfed, mom has to have a diet completely free of cow’s milk and soy. The diet is not for the faint of heart. Practically everything has milk, butter, or soy it in (not just cheese and yogurt, think breads, sauces, tofu, etc.). Frankly, my hat goes off to the moms who can do it (I don’t think I’m that disciplined). If the baby is formula fed, you have to change to hypoallergenic/hydrolyzed formulas (e.g., Alimentum and Nutramigen). On occasion, I’ll have a baby that is so bad that I have to move to an amino acid-based or elemental formula (Neocate or Puramino). Prep yourself, these are all really expensive and there isn’t a generic available. Also, FYI, the formulas generally don’t taste as good and can cause stinky poop (I mean, more than usual).
Time is a trick with MSPI. It can take a while to show up (because the gut isn’t born inflamed and damaged, it takes time for it to happen) and it takes a while to recover after the diet has been changed. So don’t expect overnight onset or improvement (generally two weeks minimum).
The good news in this miserable diagnosis is that it tends to be a problem of infants only. Most infants outgrow the intolerance by the time they are a year (some even younger).
Thanks to the parents who let me snap of a pic of the poop their baby had in clinic. It’s classic MSPI poop.