ABP Pediatric Endocrinology cheat sheet

Normal growth velocity is about 25 cm/year in the first year, 12 cm/year at 1-2 years, 7-8 cm/year at 2-4 years, 5-6 cm/year in mid-childhood, and 8-10 cm/year at the pubertal peak.

Height SDS = (patient height − population mean for age and sex) / population SD; short stature is a height below −2 SDS.

Midparental target height: boys (father + mother + 13 cm)/2; girls (father + mother − 13 cm)/2; target range is ±8.5 cm.

Bone age delay greater than 2 SD suggests constitutional delay of growth, growth hormone deficiency, hypothyroidism, or chronic disease.

Growth hormone deficiency is supported by a peak GH below 10 ng/mL on two provocative tests (clonidine, arginine, glucagon, or insulin), with assay-specific cutoffs.

Recombinant GH is dosed at about 0.025-0.05 mg/kg/day subcutaneously, with IGF-1 monitored to remain within the age- and sex-specific reference range.

All short girls need a karyotype to exclude Turner syndrome; GH is approved for Turner syndrome at up to 0.375 mg/kg/week.

Initial screening in isolated short stature: CBC, ESR, creatinine, electrolytes, celiac serology, TSH, IGF-1, and bone age radiograph.

Order of hormone loss in acquired hypopituitarism: GH first, then gonadotropins, TSH, ACTH, and ADH; congenital hypopituitarism may present with neonatal hypoglycemia, micropenis, and cholestasis.

Pituitary stalk interruption syndrome shows an ectopic posterior pituitary, a thin or absent stalk, and anterior pituitary hypoplasia on MRI.

Craniopharyngioma causes headache, bitemporal hemianopia, growth failure, obesity, and diabetes insipidus; treatment often leaves panhypopituitarism.

Prolactin above 200 ng/mL strongly suggests a prolactinoma; dopamine agonists such as cabergoline are first-line therapy.

Central diabetes insipidus shows dilute urine with high serum osmolality and responds to desmopressin; nephrogenic diabetes insipidus does not respond.

The insulin tolerance test is the gold standard for GH and ACTH reserve but is contraindicated with seizures or cardiac disease; glucagon and arginine are alternatives.

When cortisol and thyroid hormone are both deficient, glucocorticoid must be replaced before or with levothyroxine to avoid precipitating an adrenal crisis.

Septo-optic dysplasia combines optic nerve hypoplasia, midline brain defects such as an absent septum pellucidum, and hypopituitarism.

Newborn screening TSH is collected after 24-48 hours; an abnormal screen requires immediate serum free T4 and TSH testing.

Congenital hypothyroidism is treated with levothyroxine 10-15 mcg/kg/day started immediately, without waiting for imaging.

Acquired hypothyroidism in children is most often Hashimoto thyroiditis, with elevated TSH, low free T4, and positive thyroperoxidase antibodies.

Levothyroxine replacement in older children and adolescents is about 2-3 mcg/kg/day, titrated to a normal TSH.

Graves disease shows suppressed TSH, elevated free T4, diffuse goiter, and positive TSH receptor antibodies; methimazole is first-line therapy.

Propylthiouracil is avoided in children because of hepatotoxicity, but is used in thyroid storm and in the first trimester of pregnancy.

Pediatric thyroid nodules require fine-needle aspiration when at least 1 cm; malignancy risk is higher in children than in adults.

Thyroid storm management: propylthiouracil, beta-blockade, iodine given at least one hour after propylthiouracil, glucocorticoids, and supportive care.

21-hydroxylase deficiency accounts for about 95% of congenital adrenal hyperplasia; roughly 75% have salt-wasting with hyponatremia, hyperkalemia, and hypotension in the first weeks of life.

CAH treatment: hydrocortisone 10-15 mg/m2/day divided three times, fludrocortisone 0.05-0.2 mg/day, and sodium chloride supplements in infancy.

Adrenal crisis: hydrocortisone 50-100 mg/m2 IV bolus, then 50-100 mg/m2/day, with isotonic saline containing dextrose.

Primary adrenal insufficiency causes hyperpigmentation, hyponatremia, hyperkalemia, low cortisol, and elevated ACTH.

Cushing syndrome is confirmed by elevated late-night salivary cortisol, elevated 24-hour urinary free cortisol, or failure to suppress cortisol on low-dose dexamethasone testing.

Primary aldosteronism shows hypertension, hypokalemia, and elevated aldosterone with suppressed renin.

Pheochromocytoma is screened with plasma free metanephrines; associations include MEN2, VHL, NF1, and SDH mutations.

Newborn screening 17-hydroxyprogesterone is elevated in 21-hydroxylase deficiency; confirm with repeat 17-OHP, electrolytes, renin, and cortisol.

Normal puberty: breast budding at 8-13 years in girls and testicular volume above 4 mL at 9-14 years in boys; menarche follows thelarche by about 2-2.5 years.

Precocious puberty is breast development before 8 years in girls or testicular enlargement before 9 years in boys.

A pubertal LH peak (about above 5 IU/L) after GnRH agonist stimulation confirms central precocious puberty, treated with a GnRH agonist such as leuprolide.

Premature thelarche is isolated, nonprogressive, and not accompanied by accelerated growth or advanced bone age, so it requires observation only.

Delayed puberty: no breast development by 13 years in girls or no testicular enlargement by 14 years in boys.

Turner syndrome (45,X) causes gonadal dysgenesis; estrogen replacement is started around 12-13 years to induce puberty.

Klinefelter syndrome (47,XXY) causes small firm testes, gynecomastia, tall stature, and hypergonadotropic hypogonadism.

Primary amenorrhea is evaluated at 15 years, or at 13 years if secondary sexual characteristics are absent.

46,XX DSD is most often caused by congenital adrenal hyperplasia; 46,XY DSD includes androgen insensitivity, 5-alpha-reductase deficiency, and gonadal dysgenesis.

Complete androgen insensitivity: 46,XY, female phenotype, blind vaginal pouch, absent uterus, testes, normal-to-high testosterone, and elevated LH.

5-alpha-reductase deficiency: normal testosterone, low dihydrotestosterone, elevated testosterone/DHT ratio, ambiguous genitalia at birth, and virilization at puberty.

A newborn with ambiguous genitalia needs karyotype, 17-hydroxyprogesterone, electrolytes, pelvic ultrasound, testosterone, and LH; sex assignment is deferred until the workup is complete.

Persistent Müllerian duct syndrome: 46,XY with a uterus and fallopian tubes due to AMH or AMH receptor mutations.

Kallmann syndrome is hypogonadotropic hypogonadism with anosmia, caused by failed GnRH neuron migration.

Mixed gonadal dysgenesis (45,X/46,XY) carries a risk of gonadoblastoma, so gonadectomy is considered.

Turner syndrome and Klinefelter syndrome are sex chromosome DSDs; karyotype is the first-line diagnostic test.

Type 1 diabetes autoantibodies include GAD65, IA-2, ZnT8, and insulin; DKA is defined by pH below 7.3, bicarbonate below 15, and ketonemia.

DKA: give 10 mL/kg isotonic saline first, then 1.5-2 times maintenance; start insulin at 0.05-0.1 U/kg/hour after fluids.

Add dextrose to DKA fluids when glucose falls below 250-300 mg/dL so insulin can continue and ketones clear.

Cerebral edema in DKA presents with headache, bradycardia, hypertension, and altered mentation; treat with mannitol or hypertonic saline.

Neonatal diabetes from KCNJ11 or ABCC8 mutations often responds to sulfonylureas; 6q24 abnormalities cause transient neonatal diabetes.

MODY: HNF1A is sulfonylurea-sensitive; GCK causes mild stable fasting hyperglycemia that generally needs no treatment.

Hypoglycemia critical sample at glucose below 50 mg/dL: insulin, C-peptide, cortisol, GH, ketones, free fatty acids, lactate, ammonia, and acylcarnitine.

Hyperinsulinism shows high insulin with suppressed ketones and free fatty acids and high glucose requirement; treat with diazoxide or octreotide.

Nutritional rickets: low 25-hydroxyvitamin D, elevated PTH and alkaline phosphatase, and wrist metaphyseal cupping and fraying.

Corrected calcium = measured calcium + 0.8 × (4.0 − serum albumin in g/dL).

Vitamin D supplementation: 400 IU/day for infants and 600 IU/day for children and adolescents.

Vitamin D deficiency treatment: 2,000 IU/day or 50,000 IU weekly for 6-8 weeks, followed by maintenance dosing.

Hypoparathyroidism causes low calcium, high phosphate, and low PTH; DiGeorge syndrome (22q11.2 deletion) is a common cause.

Pseudohypoparathyroidism causes low calcium, high phosphate, and high PTH from GNAS mutations, with Albright hereditary osteodystrophy features.

X-linked hypophosphatemic rickets: elevated FGF23, low phosphate, high alkaline phosphatase, treated with burosumab or phosphate plus calcitriol.

Osteogenesis imperfecta: type I collagen defects with fractures, blue sclerae, and short stature; bisphosphonates reduce fracture rate.

BMI at or above the 95th percentile is obesity, 85th-95th percentile is overweight, and at least 120% of the 95th percentile is severe obesity.

Universal lipid screening is recommended at ages 9-11 years and again at 17-21 years.

LDL cholesterol above 190 mg/dL suggests familial hypercholesterolemia; statins may be started at 8-10 years.

Metabolic syndrome: central obesity plus two of triglycerides at least 150 mg/dL, HDL below 40 mg/dL, blood pressure at least 130/85, or fasting glucose at least 100 mg/dL.

Monogenic obesity genes include MC4R, leptin, and POMC; syndromic obesity includes Prader-Willi and Bardet-Biedl syndromes.

Type 2 diabetes screening begins at 10 years or at puberty in youth with BMI at or above the 85th percentile plus risk factors.

Endocrine causes of obesity to exclude: hypothyroidism, Cushing syndrome, and growth hormone deficiency.

Maintenance fluids by the 4-2-1 rule: 4 mL/kg/hour for the first 10 kg, 2 mL/kg/hour for the next 10 kg, and 1 mL/kg/hour thereafter.

SIADH: euvolemic hyponatremia, urine osmolality above 100 mOsm/kg, urine sodium above 40 mEq/L, and low serum osmolality; treat with fluid restriction.

Symptomatic hyponatremia is treated with 3% saline; correction should not exceed 8-10 mEq/L per day to prevent osmotic demyelination.

Hypernatremia is corrected by no more than 10-12 mEq/L per day to avoid cerebral edema.

Central diabetes insipidus: polyuria, dilute urine, high serum osmolality, and response to desmopressin.

Nephrogenic diabetes insipidus causes include lithium, hypercalcemia, hypokalemia, and vasopressin receptor mutations.

Cerebral salt wasting differs from SIADH by hypovolemia and high urine sodium, and is treated with saline replacement.

MEN1: parathyroid adenomas, pituitary adenomas, and pancreatic neuroendocrine tumors, from MEN1 gene mutations.

MEN2A: RET mutations with medullary thyroid carcinoma, pheochromocytoma, and hyperparathyroidism.

MEN2B: RET codon 918 mutation with medullary thyroid carcinoma, pheochromocytoma, marfanoid habitus, and mucosal neuromas; prophylactic thyroidectomy is performed early.

VHL syndrome: hemangioblastomas, pheochromocytoma, and renal cell carcinoma, from VHL gene mutations.

Neurofibromatosis type 1: café-au-lait spots, neurofibromas, optic glioma, and pheochromocytoma.

Beckwith-Wiedemann syndrome: 11p15 imprinting defect with macroglossia, omphalocele, macrosomia, neonatal hypoglycemia, and Wilms tumor risk.

Prader-Willi syndrome: loss of paternal 15q11-q13 expression with hypotonia, hyperphagia, obesity, hypogonadism, and short stature.

Li-Fraumeni syndrome (TP53) increases the risk of adrenocortical carcinoma, breast cancer, sarcoma, and brain tumors.