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Hypоpаrаthyrоidism (Study Outline) Fоr study only—this is not medicаl advice or a substitute for professional care. 1. Background Definition:A disorder characterized by deficient secretion or action of parathyroid hormone (PTH), leading to hypocalcemia and hyperphosphatemia. Pathophysiology: ↓ PTH → ↓ bone resorption of calcium, ↓ renal calcium reabsorption, ↓ activation of vitamin D → ↓ intestinal calcium absorption. Simultaneous ↑ renal phosphate reabsorption → hyperphosphatemia. Major Causes: Postsurgical (most common): accidental removal or damage to parathyroid glands during thyroid, parathyroid, or neck surgery. Autoimmune destruction: part of autoimmune polyglandular syndrome type I. Congenital: DiGeorge syndrome (22q11 deletion → absent parathyroids). Infiltrative/metabolic: hemochromatosis, Wilson disease, severe hypomagnesemia (impairs PTH secretion). Idiopathic or genetic PTH resistance: pseudohypoparathyroidism (high PTH, hypocalcemia due to end-organ resistance). Epidemiology: Uncommon; most cases are iatrogenic (post-thyroidectomy). 2. History Symptoms (due to hypocalcemia): Neuromuscular irritability: perioral or fingertip tingling, muscle cramps, carpopedal spasms. Tetany: involuntary muscle contractions, laryngospasm, or seizures in severe cases. Psychiatric: anxiety, irritability, depression. Chronic manifestations: dry skin, brittle nails, coarse hair, cataracts, dental abnormalities. Historical Clues: Recent neck or thyroid surgery. Autoimmune history (e.g., mucocutaneous candidiasis, adrenal insufficiency). Family history of congenital syndromes. 3. Exam Findings Neuromuscular Signs (classic for hypocalcemia): Chvostek sign: facial muscle contraction when tapping facial nerve (cheek). Trousseau sign: carpal spasm after inflation of BP cuff for 3 min. Cardiovascular: Hypotension, prolonged QT interval on ECG. Skin/Hair: Dry, flaky skin; brittle nails; coarse hair. Eyes: Cataracts (chronic hypocalcemia). Dentition: Enamel hypoplasia, defective root formation (pediatric cases). 4. Making the Diagnosis Key Lab Pattern (Primary Hypoparathyroidism): ↓ Serum calcium ↑ Serum phosphate ↓ or inappropriately normal PTH Normal or low magnesium (severe Mg deficiency suppresses PTH). Confirmatory Tests: Serum magnesium: to exclude Mg deficiency. Urinary calcium: may be low. Vitamin D levels: rule out deficiency. ECG: may show prolonged QT interval. If postsurgical: diagnosis is clinical (neck surgery + low calcium + low PTH).If autoimmune/genetic: test for associated antibodies or genetic deletions. Gold Standard: Low PTH with concurrent hypocalcemia and hyperphosphatemia. 5. Management (Exam Concepts) (Conceptual overview only—no dosing or treatment regimens.) Acute Hypocalcemic Crisis (Tetany/Seizure): IV calcium administration under cardiac monitoring. Chronic Management: Oral calcium supplements and activated vitamin D analogs (calcitriol) to maintain normal calcium and phosphate balance. Thiazide diuretics (conceptual) may reduce urinary calcium loss. Recombinant human PTH (rarely used): for refractory chronic cases. Correct hypomagnesemia before calcium replacement. Postsurgical Prevention: Preserve parathyroid glands during thyroidectomy. Prophylactic calcium and vitamin D in high-risk surgical patients. Exam Tips: Low Ca²⁺, high phosphate, low PTH = primary hypoparathyroidism. Low Ca²⁺, high phosphate, high PTH = pseudohypoparathyroidism (PTH resistance). Prolonged QT interval on ECG is a key clue. Most common cause = neck surgery. NBME-Style Practice Question A 46-year-old woman presents with muscle cramps and tingling around her mouth one week after total thyroidectomy. Physical exam shows facial muscle twitching when the facial nerve is tapped. Labs show: Calcium: 7.0 mg/dL (low) Phosphate: 5.8 mg/dL (high) PTH: low Which of the following is the most likely diagnosis? A. Primary hypoparathyroidismB. Secondary hyperparathyroidismC. PseudohypoparathyroidismD. Vitamin D deficiency
Vitаmin D Deficiency (Study Outline) Fоr study оnly—this is nоt medicаl аdvice or a substitute for professional care. 1. Background Definition:A condition characterized by inadequate vitamin D levels, resulting in impaired calcium and phosphate absorption, leading to secondary hyperparathyroidism, hypocalcemia, and bone demineralization. Physiology Recap: Vitamin D (cholecalciferol/ergocalciferol) is hydroxylated in the liver → 25-hydroxyvitamin D, then in the kidney → 1,25-dihydroxyvitamin D (calcitriol), the active form. Calcitriol promotes calcium and phosphate absorption in the intestine and reabsorption in the kidney, and stimulates bone mineralization. Pathophysiology: Deficiency → ↓ intestinal calcium absorption → hypocalcemia → compensatory ↑ PTH → secondary hyperparathyroidism. PTH increases bone resorption → osteomalacia (adults) or rickets (children). Causes: Inadequate intake or sunlight exposure (most common). Malabsorption (celiac disease, cystic fibrosis, bariatric surgery). Chronic kidney disease (↓ 1α-hydroxylation). Liver disease (↓ 25-hydroxylation). Medications: anticonvulsants (phenytoin, phenobarbital), glucocorticoids. Exclusive breastfeeding without supplementation in infants. Epidemiology: Common in elderly, limited sun exposure, darker skin pigmentation, and northern latitudes. 2. History Adults (Osteomalacia): Diffuse bone pain and tenderness. Muscle weakness (especially proximal). Fatigue and difficulty walking. Fractures after minimal trauma. Children (Rickets): Delayed growth, bone deformities (bowing of legs, rachitic rosary, frontal bossing). Delayed tooth eruption. Hypotonia and developmental delay (in severe cases). Historical Clues: Minimal sun exposure, low dietary intake, malabsorptive conditions, chronic kidney or liver disease, anticonvulsant use. 3. Exam Findings Adults: Bone tenderness (especially ribs, sternum, long bones). Waddling gait or difficulty rising from chair. Muscle weakness (proximal). Children: Skeletal deformities: Bowed legs (genu varum). Rachitic rosary (costochondral bead-like enlargements). Craniotabes (soft skull). Delayed fontanelle closure. Other: Signs of hypocalcemia in severe cases (Chvostek or Trousseau signs). 4. Making the Diagnosis Laboratory Pattern: Parameter Finding Calcium ↓ or low-normal Phosphate ↓ PTH ↑ (secondary hyperparathyroidism) Alkaline phosphatase ↑ (bone turnover) 25-hydroxyvitamin D (25[OH]D) ↓ (best screening test) Key Diagnostic Points: 25(OH)D < 20 ng/mL = deficiency; 20–30 = insufficiency. 1,25(OH)₂D (calcitriol) is not a good screening test — may be normal or high in early deficiency. X-rays (if bone pain/deformities): Osteopenia, Looser zones (pseudofractures), or bone bowing in children. Bone biopsy (rare): confirms osteoid accumulation (unmineralized bone). Gold Standard: Low 25-hydroxyvitamin D level with corresponding biochemical abnormalities (↑ PTH, ↓ calcium, ↓ phosphate, ↑ ALP). 5. Management (Exam Concepts) (Conceptual overview only—no dosing or treatment regimens.) General Principles: Correct vitamin D deficiency and address calcium intake. Identify and treat underlying causes (malabsorption, CKD, liver disease). Supplementation (Conceptual): Vitamin D2 (ergocalciferol) or D3 (cholecalciferol) replacement. Calcium supplementation to restore balance. Activated vitamin D (calcitriol) in chronic kidney disease (impaired conversion). Lifestyle Measures: Encourage adequate sunlight exposure (10–15 min several times/week). Balanced diet with fortified foods (milk, fish oils, eggs). Monitoring: Recheck calcium, phosphate, ALP, and 25(OH)D levels after therapy. Watch for hypercalcemia during high-dose replacement. NBME-Style Practice Question A 62-year-old woman presents with progressive muscle weakness and diffuse bone pain. She spends most of her time indoors and has a diet low in dairy. Labs show: Calcium: 8.0 mg/dL (low) Phosphate: 2.0 mg/dL (low) Alkaline phosphatase: elevated PTH: elevated 25-hydroxyvitamin D: low Which of the following is the most likely diagnosis? A. Primary hyperparathyroidismB. Osteomalacia due to vitamin D deficiencyC. Paget disease of boneD. Osteoporosis
Thyrоid Nоdules (Study Outline) Fоr study only—this is not medicаl аdvice or а substitute for professional care. 1. Background Definition:A discrete lesion within the thyroid gland that is radiologically distinct from surrounding parenchyma. Nodules may be benign or malignant, solitary or multiple. Epidemiology: Very common — detected in ~5% of adults on palpation and up to 50–60% on ultrasound. Women > men, incidence increases with age and iodine deficiency. Majority (>90%) are benign, but malignancy must be excluded. Pathophysiology / Common Types: Benign: Colloid (adenomatous) nodule — most common. Thyroid cyst (fluid-filled). Follicular adenoma. Hashimoto thyroiditis (pseudonodular changes). Malignant: Papillary carcinoma (most common). Follicular carcinoma. Medullary carcinoma (MEN 2 association). Anaplastic carcinoma (aggressive, older adults). Risk Factors for Malignancy: Prior head/neck irradiation. Family history of thyroid cancer or MEN 2. Male sex, age 60, rapid growth, hoarseness, firm/fixed mass, cervical lymphadenopathy. 2. History Common Presentations: Usually asymptomatic, found incidentally on imaging or exam. May report neck fullness or visible swelling. Compressive symptoms: dysphagia, hoarseness, choking sensation (if large or substernal). Functional symptoms: Some nodules are “hot” (toxic) — symptoms of hyperthyroidism (palpitations, heat intolerance). “Cold” nodules typically nonfunctioning — greater risk of malignancy. Historical Clues Suggesting Malignancy: Rapid growth. History of radiation exposure in childhood. Family history of medullary carcinoma or MEN 2A/2B. Persistent hoarseness or dysphagia. 3. Exam Findings Thyroid Exam: Discrete palpable nodule, may be firm or cystic. Assess for fixation to surrounding tissue or lymphadenopathy. Neck Exam: Enlarged cervical nodes (especially hard, non-tender) suggest malignancy. Voice: Hoarseness → possible recurrent laryngeal nerve involvement (red flag). Signs of Hormonal Activity: Hyperthyroidism: tachycardia, tremor, weight loss → likely “hot” nodule. Hypothyroidism: may suggest Hashimoto-related pseudonodule. 4. Making the Diagnosis Stepwise Evaluation (PANCE emphasis): 1. Measure TSH first (initial test): Low TSH: evaluate for hyperfunctioning (“hot”) nodule → perform radioactive iodine uptake (RAIU) scan. Hot nodule: increased uptake, rarely malignant. Normal or high TSH: proceed with thyroid ultrasound (US). 2. Thyroid Ultrasound Findings (high-yield): Solid > cystic composition → ↑ malignancy risk. Hypoechogenicity, microcalcifications, irregular margins, taller-than-wide shape, extrathyroidal extension, or abnormal cervical nodes → suspicious for carcinoma. 3. Fine-Needle Aspiration (FNA) Biopsy: Gold standard diagnostic test for determining malignancy. Indicated for: Nodules ≥1 cm with suspicious US features. Nodules ≥1.5–2 cm if solid and intermediate risk. Any size with abnormal lymph nodes. 4. Additional Studies: Serum calcitonin: screen for medullary thyroid carcinoma (MEN 2). Thyroglobulin: useful in postoperative monitoring, not initial diagnosis. Gold Standard: Ultrasound-guided FNA cytology. 5. Management (Exam Concepts) (Conceptual overview only—no treatment directives or dosing.) Benign Nodules: Observation with serial ultrasound every 6–12 months. Suppressive therapy (thyroid hormone) not routinely recommended. Repeat FNA if growth or new suspicious features develop. Hyperfunctioning (“Hot”) Nodules: Low malignancy risk. Manage per hyperthyroidism principles (e.g., radioactive iodine ablation or surgery if symptomatic). Malignant or Suspicious Nodules: Surgical referral for thyroid lobectomy or total thyroidectomy depending on type and size. Postoperative management may include radioactive iodine ablation and thyroid hormone replacement. Special Considerations: Pregnancy: defer radionuclide scanning; rely on US and FNA. Medullary carcinoma: evaluate for MEN 2 (check calcitonin, plasma metanephrines). QUESTION A 45-year-old woman presents with a firm thyroid nodule discovered on routine exam. TSH level is normal. Ultrasound shows a 1.5 cm solid, hypoechoic lesion with irregular margins and microcalcifications. Which of the following is the most appropriate next diagnostic step? A. Thyroid suppression therapy with levothyroxineB. Fine-needle aspiration biopsy of the noduleC. Radioactive iodine uptake (RAIU) scanD. Measurement of serum thyroglobulin level