Growth, Nutrition & Endocrine

Growth benchmarks and short stature

Normal growth. Birth weight doubles by 4–6 months and triples by 12 months, and length increases by about 50% over the first year. Serial plotting on growth charts matters more than any single point, and crossing two major percentile lines downward signals growth failure. In undernutrition weight falls first, then length, then head circumference; length falling with preserved weight-for-height suggests an endocrine cause.

Bone age anchors the workup. The key test for short stature is a bone-age radiograph of the left hand and wrist compared with chronologic age. Pair it with growth velocity and the mid-parental (genetic) target height: a normal velocity tracking along a percentile points to a normal variant, whereas a falling velocity points to an acquired or endocrine cause.

Benign variants. In constitutional growth delay, bone age lags chronologic age, so there is extra growing time and adult height is normal; familial (genetic) short stature simply tracks a short genetic target. Both have normal growth velocity and need only reassurance.

Pathologic causes drop the velocity. Growth hormone deficiency gives a low growth velocity, delayed bone age, and increased weight-for-height (a short, chubby child); screen with IGF-1 and IGF-BP3, confirm with GH stimulation testing, and image the pituitary (e.g., craniopharyngioma). Hypothyroidism and Cushing syndrome also produce a short, heavy child, whereas chronic disease (celiac disease, IBD, CKD) usually lowers weight before height.

Karyotype every unexplained short girl: Turner syndrome (45,X) can present with isolated short stature before the webbed neck, widely spaced nipples, coarctation, or absent puberty is noticed.

Puberty: normal, precocious, and delayed

Girls. Thelarche (breast bud) at 8–13 years is the first sign, followed by pubarche, the growth spurt, and menarche about 2–2.5 years after thelarche. The growth spurt comes early (Tanner 2–3).

Boys. Testicular enlargement to 4 mL (or 2.5 cm in length) at 9–14 years is the first sign. The growth spurt comes late (Tanner 3–4), so boys keep growing longer.

Precocious puberty means pubertal signs before 8 in girls or 9 in boys, with an advanced bone age. An LH level (basal or after GnRH stimulation) separates the two mechanisms. In boys, enlarged testes point to a central cause, whereas virilization with prepubertal testes points to an adrenal or exogenous androgen source.

McCune-Albright syndrome (mosaic activating GNAS mutation) combines coast-of-Maine café-au-lait macules, polyostotic fibrous dysplasia, and GnRH-independent precocious puberty. Premature thelarche and premature adrenarche are benign variants with normal growth velocity and are observed.

Delayed puberty is no breast development by 13 in girls or no testicular enlargement by 14 in boys. The most common cause is constitutional delay. Gonadotropins sort the rest: high LH and FSH mean primary hypogonadism (Turner, Klinefelter) and call for a karyotype; low levels mean constitutional delay or hypogonadotropic hypogonadism—Kallmann syndrome (GnRH deficiency with anosmia), chronic illness, anorexia, or intense athletic training.

Congenital hypothyroidism and pediatric DKA

Congenital hypothyroidism is a leading treatable cause of intellectual disability (fetal alcohol syndrome is the leading preventable cause). It is caught on the newborn screen, and thyroid dysgenesis (an absent, hypoplastic, or ectopic gland) is the leading cause. Newborns look normal at birth because maternal T4 crosses the placenta, so treatment never waits for symptoms: confirm with serum TSH and free T4 and start levothyroxine immediately to prevent irreversible neurologic damage.

Untreated signs emerge over weeks: prolonged jaundice, a large fontanelle, macroglossia, umbilical hernia, hypotonia, constipation, poor feeding, and a hoarse cry.

New-onset type 1 diabetes brings polyuria, polydipsia, weight loss, and new enuresis in a toilet-trained child, sometimes as DKA: glucose over 200 mg/dL, venous pH under 7.3 or bicarbonate under 18, an anion gap, and ketones, often with vomiting, abdominal pain, and Kussmaul breathing.

Cerebral edema is the most feared complication and the leading cause of death in pediatric DKA, often linked to overly rapid correction; bicarbonate is avoided. Headache, vomiting, declining mental status, or bradycardia with hypertension during treatment calls for immediate mannitol or hypertonic saline and slower fluids, before any imaging.

Infant nutrition and rickets

• Breastfeeding: exclusive for about 6 months, then iron-rich solids at 6 months.
• Vitamin D 400 IU daily from birth for every breastfed infant (and formula-fed infants taking <1 L/day), because breast milk is low in vitamin D.
• Vitamin K IM at birth for every newborn, because breast milk is low in vitamin K; it prevents vitamin K deficiency bleeding.
• No cow's milk before 12 months (occult GI bleeding, iron deficiency); excess cow's milk later in toddlerhood is a classic cause of iron-deficiency anemia.
• No honey before 12 months (infant botulism from Clostridium botulinum spores).

Nutritional rickets is vitamin D deficiency in the growing skeleton, classically in an exclusively breastfed, dark-skinned infant with little sun. Low calcium absorption drives high PTH, which holds calcium low-normal at the cost of renal phosphate wasting: low phosphate and a high alkaline phosphatase from unmineralized bone, with a low 25-hydroxyvitamin D. Exam shows bowed legs (genu varum), a rachitic rosary, widened wrists, frontal bossing, and craniotabes; radiographs show cupped, frayed metaphyses. Treat with vitamin D and calcium.

X-linked hypophosphatemic rickets (PHEX mutation, excess FGF23) wastes phosphate through the kidney: low phosphate with normal calcium, and no response to vitamin D. It is treated with oral phosphate plus calcitriol, or the anti-FGF23 antibody burosumab.

Obesity and severe malnutrition

Obesity. A BMI at or above the 95th percentile for age and sex is obese; the 85th–95th percentile is overweight. Complications include type 2 diabetes (acanthosis nigricans marks insulin resistance), NAFLD, slipped capital femoral epiphysis, Blount disease, obstructive sleep apnea, hypertension, and dyslipidemia. Exogenous obesity makes children tall for age; a short, obese child suggests an endocrine cause (hypothyroidism, Cushing, GH deficiency) or a syndrome such as Prader-Willi.

Refeed slowly: rapid refeeding shifts phosphate, potassium, and magnesium into cells, and refeeding syndrome—hallmarked by hypophosphatemia—can cause heart failure and arrhythmias.