Endocrinology

​Endocrinology Board Review

By MS

Multiple Choice

Most common cause of subclinical hyperthyroidism

• Toxic multinodular goiter

• Graves’ Disease

• Subacute Thyroiditis

• TSH-secreting pituitary adenoma

Multiple Choice

A 40-year-old woman with recently diagnosed primary hyperparathyroidism is evaluated with an abdominal radiograph.

Which of the following is the most likely diagnosis?

• Chronic pancreatitis

• Nephrocalcinosis

• Nephrolithiasis

• Renal cell carcinoma

• Nephrocalcinosis is calcium deposition in renal parenchyma- Mechanism: Excess PTH drives hypercalcemia and hypercalciuria, promoting calcium-phosphate deposition in tubules and interstitium

• Imaging: Ultrasound shows echogenic foci; CT/MRI define extent and guide management .

• Biochemistry: Elevated calcium, PTH, and 24-hour urine calcium > 400 mg/d support the diagnosis

• Complications: AKI, nephrolithiasis, and chronic kidney disease are common

• Management: Parathyroidectomy is definitive; hydration and bisphosphonates are adjuncts

Multiple Choice

A 43-year-old man has developed changes in skin color and is evaluated for weight loss, nausea, and weakness.

Skin findings are shown.

Which of the following is the most likely diagnosis?

• Acanthosis nigricans

• 
  Diffuse melanosis cutis

• 
  Primary adrenal insufficiency

• Secondary adrenal insufficiency

Primary adrenal insufficiency.

Physical examination is helpful in the differentiation of primary (adrenal) from secondary (pituitary) causes of adrenal insufficiency;

Only patients with primary adrenal insufficiency have excessive adrenocorticotropic hormone, melanocyte-stimulating hormone, and pro-opiomelanocortin secretion, which results in darkly pigmented skin

Multiple Choice

An 81-year-old man is evaluated for a 3-month history of fatigue, constipation, cognitive symptoms, and cold intolerance. He has gained 4.5 kg (10 lb) during the past year. Medical history is significant for CAD. Medications are rosuvastatin, lisinopril, metoprolol, and aspirin.

On physical examination, pulse rate is 54/min. Weight is 65 kg (143.0 lb). The thyroid is firm but not enlarged, the skin is cool and dry, and his hair is coarse. Deep tendon reflexes are delayed.

Laboratory studies show a thyroid-stimulating hormone level of 25 µU/mL and free thyroxine level of 0.5 ng/dL (0.9-1.4)

Most appropriate treatment?

• Levothyroxine, 25 μg/d

• 
  Levothyroxine, 100 μg/d

• Thyroid, desiccated, 60 mg/d

• 
  Triiodothyronine, 50 μg/d

• Treatment: Levothyroxine is first‑line for hypothyroidism

• Dose: Full replacement ≈ 1.6 μg/kg (lean body weight)

• Exceptions: Start low (25–50 μg/day) in older adults or CAD

• Rationale: Thyroid hormone ↑ cardiac demand → risk of angina

Multiple Choice

A 40-year-old woman with symptoms of hyperthyroidism and a suppressed thyroid-stimulating hormone level is evaluated for a left thyroid nodule. Thyroid scintigraphy is performed.

Dx?

• 
  Autonomously functioning thyroid adenoma

• Graves disease

• 
  Multinodular goiter

• Thyroid cancer

• Diagnosis: Autonomously functioning thyroid adenoma (toxic nodule)

• Key labs: Suppressed TSH

• Next test: Thyroid scintigraphy

• Finding: “Hot” nodule with increased radioactive iodine uptake

• Management: Usually benign → no biopsy needed

• Ex: "cold" nodule is below

Multiple Choice

A 55-year-old man is evaluated for a 1-year history of decreased libido, erectile dysfunction, and fatigue. Medical history is also significant for opioid use disorder treated with methadone. He takes no other medications. On physical examination, vital signs are normal. BMI is 25. The remainder of the examination, including genital and prostate examination, is normal. A morning testosterone level obtained 4 weeks ago is low. Pituitary MRI is normal.

Laboratory studies:

Hemoglobin Normal

Follicle-stimulating hormone 2.1 mU/mL (5-15)

Luteinizing hormone 1.4 mU/mL (3-15)

Prolactin 18 ng/mL (<15)

Testosterone, total (8 AM) (second measurement) 140 ng/dL (300-1200)

Which of the following is the most appropriate treatment?

• Alprostadil

• Cabergoline

• Sildenafil

• Testosterone

• Chronic opioids leads to ↓ GnRH → ↓ LH/FSH → secondary hypogonadism

• Additional: Opioids may ↑ prolactin → further GnRH suppression

• Clinical:

  • Men: ↓ libido, ED, fatigue, low testosterone with low/normal LH/FSH

  • Women: Menstrual irregularities

• Management:

  • Stop opioids if possible

  • If not → testosterone replacement in symptomatic men

• Why not others:

  • Alprostadil / PDE‑5 inhibitors: improve erections only

  • Cabergoline(D2 agonist): unlikely to reverse opioid‑induced hypogonadism

Multiple Choice

A 52-year-old man with type 2 diabetes mellitus is evaluated after hospitalization for a non-ST-elevation myocardial infarction. He is currently asymptomatic. Medications are metformin, aspirin, ticagrelor, atorvastatin, metoprolol, and lisinopril.

On physical examination, vital signs are normal. BMI is 28. The general physical examination is normal.

Laboratory studies show a hemoglobin A_1c level of 7.0%.

Which of the following is the most appropriate treatment?

• Empagliflozin

• Pramlintide

• Sitagliptin

• No changes in medications

Key Point

• Among patients with type 2 diabetes mellitus who have established atherosclerotic cardiovascular disease or established kidney disease, a sodium-glucose cotransporter 2 inhibitor or glucagon-like peptide 1 receptor agonist with demonstrated cardiovascular disease benefit is recommended as part of the glucose-lowering regimen.

Multiple Choice

A 61-year-old woman is evaluated after an abdominal CT scan for diverticulitis revealed an incidental adrenal mass. She has no other medical problems and takes no medications.

On physical examination, vital signs are normal. The remainder of the examination is unremarkable.

Abdominal CT scan shows a 3.5-cm homogeneous left adrenal mass with a density of 13 Hounsfield units. The remainder of the scan is normal.

Serum creatinine and electrolytes are normal. Testing for mild autonomous cortisol secretion is negative.

Which of the following is the most appropriate next step in management?

• Adrenal biopsy

• Adrenalectomy

• 
  Screening for primary aldosteronism

• Screening for pheochromocytoma

Key Points

• In patients with incidentally noted adrenal masses, screening for pheochromocytoma is indicated if the unenhanced CT attenuation is greater than 10 Hounsfield units.

• In patients with an adrenal mass, screening for primary hyperaldosteronism is indicated in the presence of hypertension or hypokalemia.

Multiple Choice

A 38-year-old-woman is evaluated for a 9-month history of oligomenorrhea, a deepening voice, and increased body hair. Her last menses was 3 months ago. Medical history is otherwise unremarkable, and she takes no medications.

On physical examination, vital signs are normal. She has frontal hair loss and coarse dark hairs on her chin and chest. Larynx appears larger than normal. Clitoromegaly is present on pelvic examination.

Laboratory studies show a negative pregnancy test, a dehydroepiandrosterone sulfate level of 910 μg/dL (24.7 μmol/L), and a total testosterone level of 97 ng/dL (3.4 nmol/L).

Which of the following is the most appropriate diagnostic test to perform next?

• Abdominal CT

• Adrenal vein sampling

• 
  Ovarian vein sampling

• Pelvic ultrasonography

• Pituitary MRI

• New hyperandrogenism (premenopausal): Evaluate ovarian + adrenal sources

• Key lab: Markedly ↑ DHEAS with mild ↑ testosterone → adrenal source

• Threshold: DHEAS >700 μg/dL → abdominal CT next

• Rationale: Adrenal androgen‑secreting tumors cause virilization and are CT‑visible

• PCOS: oligomenorrhea, hirsutism, and acne,

  but no deepening voice, clitoromegaly, frontal hair loss

Multiple Choice

A 73-year-old woman is evaluated in the emergency department after 2 days of weakness, headache, and nausea. She underwent uncomplicated transsphenoidal resection of a pituitary macroadenoma 6 days ago and was discharged from the hospital 3 days ago.

On physical examination, vital signs are normal. No orthostasis and no neurologic or visual deficits are present. Her mucous membranes are moist.

Laboratory studies show a serum sodium level of 128 mEq/L (35–145 mEq/L], TSH of 0.9 μU/mL ( 0.4–4.0 μU/mL], and free thyroxine level of 1.1 ng/dL( 0.8–1.8 ng/dL]. Before discharge, her 8 AM serum cortisol level was 15 μg/dL ( 5–25 μg/dL], and a random serum cortisol level at 3 PM was 10 μg/dL( 3–15 μg/dL].

• 
  Adrenal insufficiency

• 
  Dehydration

• Secondary hypothyroidism

• SIADH

• Diagnosis: SIADH after recent pituitary surgery

• Timing: Occurs 4–12 days postop (peak 7–8 days)

• Mechanism: Excess ADH release from posterior pituitary manipulation

• Pattern: May be part of triphasic response (DI → SIADH → permanent DI)

• Management: Fluid restriction; severe cases → hypertonic saline or vaptans

• Disposition: Admit if symptomatic or Na <130 mEq/L

• Why not others: Cortisol, volume status, and thyroid function are normal

Multiple Choice

A 32-year-old woman is evaluated in the first trimester of pregnancy for a 2-week history of heat intolerance, palpitations, and tremulousness. Her only medication is folic acid.

On physical examination, pulse rate is 110/min; remaining vital signs are normal. The thyroid is nontender and symmetrically and diffusely enlarged. A fine tremor on the patient's outstretched hands is noted.

Laboratory studies show a thyroid-stimulating hormone level of less than 0.01 μU/mL (0.4–4.0 μU/mL) and free thyroxine level of 5.3 ng/dL (0.8–1.8 ng/dL).

Which of the following is the most appropriate diagnostic test?

• Thyroid scintigraphy with radioactive iodine uptake

• 
  Thyroid-stimulating immunoglobulin measurement

• 
  Thyroid ultrasonography

• Total triiodothyronine measurement

• Diagnosis: Hyperthyroidism (↓ TSH, ↑ free T4/T3)

• Best next test: TSI or TRAb to evaluate for Graves disease

• Rationale: RAIU confirms cause but is contraindicated in pregnancy

• Alternatives:

  • hCG‑mediated hyperthyroidism or thyroiditis → often transient

• Not helpful:

  • Thyroid US alone (nonspecific for cause)

  • Total T3 (already elevated free T4; altered in pregnancy)

Multiple Choice

A 28-year-old woman is evaluated for a 6-month history of amenorrhea. Medical history is significant for schizophrenia. Her only medication is risperidone.

On physical examination, vital signs are normal. BMI is 28. No breast discharge is evident.

Laboratory studies:

Estradiol
10 pg/mL (50–100 pg/mL)

Follicle-stimulating hormone
1 mU/mL (5–50 mU/mL)

Prolactin
150 ng/mL (10–0 ng/mL)

Thyroid-stimulating hormone
2.2 μU/mL (0.4–4.0 μU/mL)

Thyroxine, free
1.2 ng/dL (0.8–1.8 ng/dL)

MRI reveals a normal pituitary gland.

Consultation with the patient's psychiatrist confirms that risperidone cannot be discontinued.

Which of the following is the most appropriate management?

• Begin cabergoline

• Begin estrogen-progesteron replacement therapy

• Repeat pituitary MRI in 6 months

• Repeat prolactin measurement in 6 months

• Risperidone‑induced hyperprolactinemia → estrogen deficiency

• Symptoms: Amenorrhea ± galactorrhea; risk of bone loss

• Best management: Estrogen–progesterone replacement therapy

• Why: Prevents long‑term sequelae of hypoestrogenism while risperidone continues

• Avoid: Dopamine agonists (eg, cabergoline) → risk of psychosis

• Not appropriate: Repeat MRI or watchful waiting without hormone replacement

Multiple Choice

A 30-year-old woman is evaluated for a 2-month history of anorexia, insomnia, palpitations, diarrhea, and an 11-kg (24.0-lb) weight loss. She reports no neck pain. She has been well otherwise and takes no medications.

On physical examination, temperature is 37.9 °C (100.0 °F), blood pressure is 118/78 mm Hg, and pulse rate is 101/min. BMI is 18. The thyroid is firm and not enlarged, with the left lobe larger than the right. No proptosis, thyroid nodules, or adenopathy are noted, and no thyroid tenderness is present.

Laboratory studies:

Thyroid-stimulating hormone
0.02 μU/mL (0.4–4.0 μU/mL)

Thyroxine, free
2.8 ng/dL (0.8–1.8 ng/dL)

Erythrocyte sedimentation rate
53 mm/h (<20 mm/h)

Human chorionic gonadotrophin: Negative

The radioactive iodine uptake scan is shown. Uptake at 24 hours is 0.3%. Which of the following is the most appropriate treatment?

• 
  Atenolol

• Methimazole

• 
  Prednisone

• 
  Propylthiouracil

• Presentation: Thyrotoxicosis (↓ TSH, ↑ free T4)

• RAIU: Low uptake → destructive thyroiditis, not Graves

• Supporting clues: No proptosis, ↑ ESR

• Pathophysiology: Release of preformed thyroid hormone

• Management: β‑blocker (atenolol) for adrenergic symptoms

• Not indicated: Methimazole/PTU (no excess hormone production), prednisone (no thyroid pain)

Multiple Choice

A 39-year-old woman is evaluated for high-risk metastatic papillary carcinoma. She had a total thyroidectomy and iodine 131 ablation therapy 6 months ago. She is now taking levothyroxine. She is asymptomatic.

On physical examination, vital signs are normal. She has a well-healed thyroidectomy scar. There are no palpable neck masses, no adenopathy, and no tremor.

Laboratory studies:

Thyroid-stimulating hormone
0.02 μU/mL (0.5–5.0 mU/L)

Thyroxine, free
1.5 ng/dL (0.8–1.8 ng/dL)

Thyroglobulin: Absent

Antithyroglobulin antibodies: Negative

Neck ultrasound is normal.

Which of the following is the most appropriate management?

• Decrease levothyroxine

• Discontinue levothyroxine

• Thyroid scintigraphy with radioactive iodine uptake

• No change in treatment

Papillary thyroid cancer:

• Primary treatment: Surgical resection is the cornerstone of thyroid cancer management

• Adjuvant therapy: Radioactive iodine for high‑risk differentiated thyroid cancer

• Long‑term management: TSH suppression with levothyroxine in high‑risk patients

• After Tx, serum thyroglobulin (Tg), a sensitive marker for the detection of persistent or recurrent disease, and thyroglobulin antibody (TgAb) titers are monitored

Multiple Select

A 58-year-old woman presents with 1 week of palpitations and dyspnea after a similar self-limited episode 3 weeks earlier with a negative CT angiogram. She takes no medications.

Vitals show BP 150/80 mm Hg and an irregularly irregular pulse of 102/min; oxygen saturation is 95%. Exam is notable for atrial fibrillation and a large multinodular goiter.

Labs reveal suppressed TSH (<0.01 μU/mL) with elevated free T4 and total T3. ECG confirms atrial fibrillation.

Which of the following is the most appropriate initial step in management? (Choose 2)

• Amiodarone

• Methimazole

• CT neck w/w out contrast

• Propranolol

• Radioactive iodine

• Iodine‑induced hyperthyroidism (Jod‑Basedow phenomenon) after iodinated contrast in multinodular goiter

• Timing: Thyrotoxicosis occurs 1–2 weeks after iodine exposure

• Management: Methimazole to block thyroid hormone synthesis + propranolol for symptom control

• Prevention: Avoid iodinated contrast and other iodine sources (amiodarone) when possible in multinodular goiter

Multiple Choice

An 83-year-old asymptomatic woman is found to have low TSH on AWE. History includes chronic stable angina and osteoporosis; she takes metoprolol, lisinopril, simvastatin, aspirin, vitamin D3, and alendronate.

Vitals are normal. The exam shows a firm, enlarged thyroid with right-sided predominance.

Subsequent labs reveal persistently suppressed TSH 0.05 μU/mL (multiple eval) with normal free T4 and total T3. Thyroid scan is provided, and 24-hour radioactive iodine uptake is 22%.

Which of the following is the most appropriate management?

• Repeat thyroid-stimulating hormone test in 6 weeks

• Start methimazole

• Start prednisone

• Start teprotumumab

• Diagnosis: Subclinical hyperthyroidism from toxic multinodular goiter (TSH < 0.1, normal T4/T3)

• Risk: Increased atrial fibrillation, CV events, bone loss with persistent TSH suppression

• Best management: Start methimazole to normalize thyroid function

• Why not observe: TSH suppressed for 8 weeks (TSH<0.1), with high cardiac risk

• Not indicated: Prednisone (no thyroiditis), teprotumumab (no Graves/ophthalmopathy)

Multiple Choice

A 56-year-old hospitalized man is evaluated for abnormal thyroid tests one week after admission for E. coli urosepsis. He is receiving IV fluids, norepinephrine, and ceftriaxone.

Vitals show hypotension and tachycardia; exam reveals cool, dry skin without goiter or proptosis. TSH is low (0.11 μU/L) with mildly decreased free T4 (0.8 ng/dL). Which of the following is the most appropriate management?

• Initiate levothyroxine

• 
  Initiate methimazole

• 
  Pituitary MRI

• 
  Thyroid testing after recovery

• Key point: Avoid routine thyroid testing in hospitalized/critically ill patients

• Diagnosis: Nonthyroidal illness syndrome (NTIS) (75% of hospitalized)

• Typical labs: Low or low‑normal TSH, normal/low free T4, low T3, high reverse T3 (inactive form)

• Mechanism: Adaptive response to illness; dopamine also can further suppress TSH

• Management: No treatment; recheck TSH in ≈6 weeks after recovery

• Not indicated now: Levothyroxine, methimazole, or pituitary MRI

Multiple Choice

A 55-year-old man reports recurrent neuroglycopenic symptoms over the past month, including a fingerstick glucose of 46 mg/dL during one episode, with relief after eating. He takes no medications.

Exam and vitals are normal; BMI is 33. Random glucose is 78 mg/dL, hemoglobin A1c is 4.7%, and other labs are normal.

Which of the following is the most appropriate diagnostic test?

• 72-Hour fast

• Mixed meal test

• Oral glucose tolerance test

• 
  Pancreatic imaging study

• Fasting hypoglycemia: Rare without diabetes → requires evaluation

• Causes: Medications, alcohol, renal/hepatic failure, adrenal insufficiency, malnutrition, prior Roux‑en‑Y gastric bypass, insulinoma (rare)

• Best test: 72-hour supervised fast with insulin, C-peptide, proinsulin, and β-hydroxybutyrate at hypoglycemia

• Indications: Document Whipple's triad or glucose ≤ 45 mg/dL with neuroglycopenia

• Exclude: Medications, alcohol, liver/renal disease, adrenal insufficiency, malnutrition, prior bariatric surgery

• Imaging: Only after biochemical confirmation of endogenous hyperinsulinism

• Not indicated: Mixed meal test (postprandial), OGTT (diabetes), or imaging before biochemical proof

Multiple Choice

A 73-year-old woman on amiodarone for atrial fibrillation presents with recurrent AF after 1 year of therapy. She has no other medical issues or iodine exposure.

Exam shows an irregular tachycardia without thyroid abnormalities. Labs reveal suppressed TSH (<0.01 μU/mL) and elevated free T4 (3.5 ng/dL); ECG confirms atrial fibrillation. Which of the following is the most appropriate diagnostic test?

• Serum thyroglobulin measurement

• 
  Thyroid peroxidase antibody titer

• Thyroid scintigraphy with radioactive iodine uptake

• 
  Thyroid ultrasonography with Doppler studies

• Thyrotoxicosis in a patient on amiodarone

• Best next test: Thyroid ultrasound with Doppler

• Purpose: Distinguish AIT types

  • Type 1 AIT → ↑ vascularity (iodine‑induced hyperthyroidism in Graves disease or thyroid nodules) Tx: methimazole

  • Type 2 AIT → ↓ vascularity (destructive thyroiditis). Tx: self-limiting

• RAIU: Unreliable due to iodine load from amiodarone

• Management: Depends on AIT type and cardiac status (coordinate with cardiology)

• ⬆️Thyroglobulin=⬆️ endogenous production

Multiple Choice

A 48-year-old woman is evaluated for a 6-month history of a 9.1-kg (20.1-lb) weight gain and easy bruising. She has newly diagnosed type 2 diabetes mellitus treated with metformin.

On physical examination, vital signs are normal. BMI is 38. The patient has central obesity, supraclavicular and dorsocervical fat pads, and wide violaceous striae on her abdomen.

Laboratory studies show elevated 24-hour urine free cortisol and late-night salivary cortisol levels.

Which of the following is the most appropriate diagnostic test to perform next?

• Abdominal CT

• Adrenocorticotropic hormone level measurement

• 8-mg Dexamethasone suppression test

• Inferior petrosal sinus sampling

• Next test: ACTH level to classify Cushing syndrome

• Diagnosis confirmed: ≥2 abnormal tests (↑ urine free cortisol, ↑ late‑night salivary cortisol)

• Purpose of ACTH: Distinguish ACTH‑dependent vs ACTH‑independent disease

• If ACTH suppressed (<5 pg/mL): ACTH‑independent → adrenal CT/MRI

• If ACTH normal/high: ACTH‑dependent → further localization

• Not indicated now:

  • Adrenal imaging (before ACTH result)

  • High‑dose dexamethasone test (only if ACTH‑dependent, no pituitary lesion)

  • Inferior petrosal sinus sampling (pre‑surgical confirmation only)

Multiple Choice

A 72-year-old man is evaluated following surgical fixation of a right distal radius fracture after a fall. Dual-energy x-ray absorptiometry (DEXA) scan performed 2 years ago showed low bone mineral density (BMD). Alendronate weekly was initiated after the scan, and he has been adherent to therapy. Review for secondary causes of osteoporosis is negative. DEXA reassessment shows no significant change in BMD. Which of the following is the most appropriate management?

• Add calcium and vitamin D supplementation

• Continue alendronate

• Order dual-energy x-ray absorptiometry scan of the distal left radius

• Measure serum C-telopeptide of type 1 collagen

• Best management: Continue alendronate

• Rationale:

  • Incident fracture ≠ treatment failure

  • No significant decline in absolute BMD

  • Fracture risk reduction not fully reflected by BMD changes

• Why not others:

  • Calcium/Vit D: supplement only if intake deficient

  • Repeat or distal radius DXA: no meaningful BMD change; high measurement error

  • Bone turnover markers (eg, C‑telopeptide): unreliable after recent fracture

Multiple Choice

A 46-year-old man is evaluated for a thyroid nodule discovered 2 years ago. Thyroid ultrasonography performed at that time showed a 2.5-cm left upper pole isoechoic solid nodule without microcalcification or irregular margin. The sonographic pattern was characterized as low suspicion for malignancy. Fine-needle aspiration biopsy showed benign cytology.

Today, on physical examination, vital signs are normal. A 2.5-cm left upper pole thyroid nodule is firm and mobile. No lymphadenopathy is evident.

Laboratory studies show a normal TSH. Which of the following is the most appropriate next step in management?

• Fine-needle aspiration biopsy

• Levothyroxine initiation

• Thyroid scintigraphy with radioactive iodine uptake

• 
  Thyroid ultrasonography

• 
  No further evaluation

• Next step for thyroid nodule: Repeat thyroid ultrasonography

• Context: Persistent 2.5‑cm nodule with prior benign FNAB and normal TSH

• Rationale:

  • Benign cytology still carries 2–7% malignancy risk

  • ATA recommends surveillance US (timing based on sonographic risk)

• Why not others:

  • Repeat FNAB: only if growth or new suspicious features

  • Levothyroxine: may help to reduce nodule growth, however ↑ risk of thyrotoxicosis

  • RAIU scan: only for suppressed TSH

  • No follow‑up: inappropriate due to false‑negative risk

Multiple Choice

A 46-year-old woman presents with a 1-year history of A 46-year-old woman presents with a 1-year history of progressive weight‑bearing leg pain and episodic chest pain with prolonged soreness. She has muscle weakness, a waddling gait, weight loss, and postprandial bloating, and takes no medications.

Exam shows bilateral rib tenderness. Labs reveal elevated alkaline phosphatase with low calcium and phosphorus; creatinine is normal. Rib radiograph shows unhealed fractures. Whole-body bone scan shows increased uptake of technetium throughout the skeleton and foci of intense uptake in the ribs and pubic rami bilaterally. Dx?

• Bone metastases

• Osteomalacia

• Osteonecrosis

• Osteoporosis

• Osteomalacia

  • Diffuse bone pain and skeletal tenderness

  • Low BMD in setting of malabsorption (eg, celiac disease, gastric bypass)

  • ↑ alkaline phosphatase (early marker)

• Supporting labs:

  • Very low 25‑hydroxyvitamin D

  • Secondary hyperparathyroidism.

  • Low urine calcium

• Bone scan: Diffuse skeletal uptake + focal hotspots → osteomalacia

• Why not others: Metastases: focal uptake, often hypercalcemia

  • Osteonecrosis: focal, not diffuse

  • Osteoporosis: does not explain diffuse uptake or biochemical abnormalities

XLH: X-Linked Hypophosphatemia
TIO: Tumor-Induced Osteomalacia