Cow's milk protein allergy (CMPA) may cause gastrointestinal motility disorders. Symptoms of both conditions overlap and diagnostic tests do not reliably differentiate between both. A decrease of symptoms with an extensive hydrolysate and relapse during challenge is not a proof of allergy, because hydrolysates enhance gastric emptying, a pathophysiologic mechanism of gastro-oesophageal reflux (GER). Thickened formula reduces regurgitation, and failure to do so suggests CMPA. A thickened extensive hydrolysate may induce more rapid improvement, but does not always differentiate between CMPA and GER. Different hypotheses are discussed: is the overlap between CMPA and functional disorders coincidence, or do both entities present with identical symptoms, or does the fact that symptoms are identical indicates that there is only one entity involved? Studies on the prevention of CMPA focused on 'at-risk families', and resulted in a decrease of CMPA and atopic dermatitis, but did not provide data on the incidence of GER.
As long as there are no objective diagnostic tools to separate GER from CMPA, the physician has two options: first treat the most likely diagnosis, and switch if after 2-4 weeks there is no improvement, or treat both conditions with one intervention, what will not result in a diagnosis.