Medical mystery | What did this teen’s weight loss have to do with allergies?

A 15-year-old girl had been training all summer at field hockey camp and was eager to start the pre-season practices in August. But first, she needed to get a sports physical.

At the appointment, her mother told the doctor that she worried about her daughter’s diet after noticing she didn’t seem to care much for fruits and veggies. But the girl said that she was avoiding certain foods because they made her throat feel itchy.

Hearing about her patient’s itchy throat made the doctor concerned about anaphylaxis, a full body allergic reaction to food. But the patient did not report any other symptoms like difficulty breathing, abdominal pain, vomiting, or hives — just the itchy throat.

To be safe, the doctor prescribed an epinephrine auto injector (better known as an EpiPen) to use in case of an emergency involving any of these additional symptoms. She also told the girl and her mother to go to the nearest emergency department right away if she needed to use the epinephrine.

The girl had lost five pounds since her last visit, and said she was exercising for several hours every day. The doctor asked about a possible eating disorder, but the patient said she didn’t have any body image concerns and was not skipping meals, bingeing, purging, or obsessing over food labels, calories, or daily weigh-ins.

What’s more, when the doctor asked the girl what she had eaten over the last 24 hours, she listed fried foods and brownies — certainly not a typical diet for a patient with anorexia nervosa. And as the mom said, fruits and vegetables weren’t on the list.

» READ MORE: What to know about eating disorders

So the next consideration was a different type of eating disorder known as Avoidant Restrictive Food Intake Disorder (ARFID), which can follow an experience with a food like feeling the throat closing. ARFID is not diagnosed when the avoidance is due to another medical condition, so the PCP kept the diagnosis of ARFID on the back burner.

The field hockey camp gave the athletes sliced apples at breaks, which the girl ate because she was hungry and needed energy, even though apples made her throat itch. A clue to the patient’s diagnosis was that she had seasonal allergies: she experienced a runny and itchy nose when the pollen count was high.

The patient’s diagnosis was Pollen Food Allergy Syndrome (PFAS). PFAS is common, particularly in adults, but can also occur at younger ages. A person with PFAS will have a reaction in their mouth and/or throat to certain fruits and vegetables. Common culprits include apples, peaches, melons, and cherries. Usually, it is not a dangerous reaction.

As the name suggests, PFAS happens to some people who have pollen allergies, even if their pollen allergies are not very severe. With pollen allergies, the immune system recognizes pollens as harmful invaders and releases histamines which cause runny noses or itchy eyes. In people with PFAS, the immune system mistakenly recognizes certain foods as harmful because some of the molecules in the food are chemically similar to molecules in pollen.

Sometimes patients with PFAS experience other systemic symptoms, most commonly gastrointestinal symptoms like nausea, abdominal discomfort, and diarrhea. Rarely, symptoms include hives (urticaria), swelling (angioedema), sneezing, flushing, wheezing, coughing, and low blood pressure. True anaphylaxis can occur but is quite rare.

Certain factors may make a PFAS patient more likely to suffer widespread reactions. These include consuming the problematic food along with the presence of “cofactors,” such as exercise or nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, presumably due to a transient increase in stomach or gut permeability.

As it turns out, the patient had taken ibuprofen for sore muscles and did have abdominal pain when she resumed exercising. PFAS can sometimes progress over the years and cause more systemic symptoms. The patient’s physician referred her to an allergist for specialized testing.

Footnote (or rather “food note”): Cooking can often change the shape of molecules so they are no longer mistaken for pollen molecules. That’s why some people with PFAS will have an itchy mouth when eating a raw apple but have no problems eating apple pie. Hearing this made the patient very happy and looking forward to dessert at the next holiday meal.

Samantha Starkey is a pediatric resident and Rima Himelstein is an adolescent medicine specialist at Nemours Children’s Health, Delaware.