Physicians must avoid getting trapped inside a diagnostic box, Harvard University professor Jerome Groopman puts forth in his recent book How Doctors Think. One case from my practice illustrates how easily we can get snared.

Familial short stature

“Joshua” was a full-term infant delivered vaginally weighing 3,280 g with APGARs of 8 and 8. He was breastfed for the first six months and then transitioned to formula and solid foods. I saw him for a variety of minor pediatric illnesses over his first 5 years — recurrent otitis media, upper respiratory tract infections, strep pharyngitis and gastroenteritis. He recovered from them all without sequelae. Subsequently, he was rarely ill and he became very athletic. Of his two older brothers, one had congenital aortic valvar stenosis and asthma, while the other was healthy.

Frankly, Joshua was indistinguishable from other patients in my practice. There was one notable exception: he was always on the short side. This came as no surprise, though — his grandparents and his parents were short, with Dad at 5'6", Mom 5'3", and his brothers, 5'5" and 5'6". “Familial short stature is by far the most common cause of short stature in the developed world. Children with this condition have a family history of short but otherwise healthy parents.” (Osborne, Pediatrics, p.1012). I was overtaken by paradigm thinking. Joshua seemed to fit the expectations connected with this strong familial trait. Using a formula for the prediction of adult height, the boy was destined to be around 164 cm as an adult.

At age 12, with a pubertal staging of Tanner 1 (prepubertal), his growth appeared to slow and his height fell slightly from its previous trajectory, although he still seemed on target to reach his predicted adult height. Despite the comfort of paradigm thinking, I also noticed my patient had constitutionally delayed puberty!

At this point, I took note of information recorded in his chart some years earlier: mother, grandmother and a male first cousin all had hypothyroidism diagnosed as adults. Joshua's thyroid was normal. But because of the family history, his mother requested a thyroid study. Results were a surprise (too much paradigm thinking!). The answer to his fall-off in growth: TSH 100 mlU/L (normal = 0.34-5.60 mIU/L) T4 = 3.1 pmol/L (normal = 8.0-18.0 pmol/L). Joshua was started on synthroid, his growth has picked up and is back on course to reach the lower end of his predicted adult height range.

Yes, Joshua had familial short stature but thinking inside this box prevented me from considering that he also had hypothyroidism!