4.4 Thyroid Disorders & Adrenal Gland Dysfunction
Key Takeaways
- Primary Hypothyroidism presents with elevated TSH and low free T4 (most commonly Hashimoto's thyroiditis with anti-TPO antibodies), whereas Primary Hyperthyroidism presents with suppressed TSH and elevated free T4/T3 (most commonly Graves' disease with TSH receptor antibodies).
- Thyroid Storm management requires a mandatory sequence: 1. Beta-blockers (Propranolol), 2. Thionamides (PTU/Methimazole), 3. Iodine solutions (SSKI/Lugol's given ≥1 hour AFTER thionamides), and 4. Hydrocortisone.
- Primary Adrenal Insufficiency (Addison's disease) involves destruction of all adrenal cortical zones, producing skin hyperpigmentation, hyponatremia, hyperkalemia, and postural hypotension; diagnosed via Cosyntropin (ACTH) stimulation testing.
- Cushing's Syndrome evaluation requires initial screening (24h UFC, 1mg DST, or late-night salivary cortisol), followed by plasma ACTH to separate ACTH-independent from ACTH-dependent causes (differentiated by 8mg high-dose DST).
- Pheochromocytoma management mandates strict Alpha-adrenergic blockade (Phenoxybenzamine) for 10-14 days BEFORE initiating Beta-blockade to avoid precipitating unopposed alpha-mediated hypertensive crisis.
Thyroid Disorders & Adrenal Gland Dysfunction
Endocrine pathology involving the thyroid and adrenal glands constitutes a cornerstone of the UPSC CMS General Medicine examination. Mastering hormone profiles, diagnostic algorithms, and acute medical emergencies is essential.
1. Thyroid Function Test Patterns & Clinical Conditions
The initial evaluation of thyroid status relies on serum Thyroid-Stimulating Hormone (TSH) (the most sensitive screening test) and Free Thyroxine (FT4) / Free Triiodothyronine (FT3).
| Diagnostic Pattern | Serum TSH | Free T4 Level | Free T3 Level | Primary Clinical Etiologies |
|---|---|---|---|---|
| Primary Hypothyroidism | Elevated (>4.5 mIU/L) | Low | Low or Normal | Hashimoto's Thyroiditis, Post-RAI ablation, Iodine deficiency |
| Subclinical Hypothyroidism | Elevated | Normal | Normal | Early Hashimoto's thyroiditis |
| Primary Hyperthyroidism | Suppressed (<0.01 mIU/L) | Elevated | Elevated | Graves' Disease, Toxic Multinodular Goiter, Toxic Adenoma |
| Subclinical Hyperthyroidism | Suppressed | Normal | Normal | Exogenous levothyroxine over-suppression, early Graves' |
| Central (Secondary) Hypothyroidism | Low or Normal | Low | Low | Pituitary adenoma, Sheehan syndrome, craniopharyngioma |
| T3 Toxicosis | Suppressed | Normal | Elevated | Early Graves' disease or autonomous T3-secreting nodule |
2. Graves' Disease vs. Hashimoto's Thyroiditis
A. Graves' Disease
- Pathophysiology: Autoimmune disease caused by Thyroid-Stimulating Immunoglobulins (TSI) / TSH Receptor Antibodies (TRAb) that stimulate the TSH receptor, causing autonomous thyroid hormone synthesis.
- Pathognomonic Features:
- Graves' Ophthalmopathy: Proptosis, exophthalmos, lid lag, extraocular muscle swelling (driven by T-cell infiltration and glycosaminoglycan deposition in retro-orbital tissue).
- Pretibial Myxedema: Non-pitting infiltrative dermopathy over anterior shins.
- Radioactive Iodine Uptake (RAIU): Diffuse, homogeneous increased uptake.
- Medical Treatment:
- Methimazole: First-line antithyroid drug for non-pregnant adults.
- Propylthiouracil (PTU): Preferred during the first trimester of pregnancy (due to methimazole embryopathy risks like aplasia cutis and choanal atresia) and in Thyroid Storm.
B. Hashimoto's Thyroiditis (Chronic Autoimmune Thyroiditis)
- Pathophysiology: Most common cause of hypothyroidism in iodine-sufficient areas. Marked by anti-Thyroid Peroxidase (anti-TPO) and anti-Thyroglobulin (anti-Tg) antibodies.
- Histology: Dense lymphocytic infiltrate with germinal centers, lymphoid follicles, and Hürthle cells (eosinophilic metaplastic follicular epithelial cells).
- Complications: Increased risk of Primary Thyroid Lymphoma (Diffuse Large B-Cell Lymphoma).
- Treatment: Levothyroxine (T4) (1.6 mcg/kg/day, taken on an empty stomach 30–60 minutes before breakfast).
3. Thyroid Emergencies: Thyroid Storm vs. Myxedema Coma
A. Thyroid Storm (Thyrotoxic Crisis)
Life-threatening hypermetabolic state triggered by infection, surgery, trauma, or RAI in uncontrolled hyperthyroidism. Diagnosed clinically via the Burch-Wartofsky Point Scale (fever >39°C, severe tachycardia/afib, agitation/delirium, jaundice, diarrhea).
UPSC CMS Mandatory Treatment Sequence for Thyroid Storm:
- Step 1: Beta-Blockers (Propranolol 60–80 mg PO q6h or IV): Controls adrenergic hyperactivity and blocks peripheral conversion of T4 to T3.
- Step 2: Thionamides (PTU 200 mg q4h or Methimazole 20 mg q6h): Blocks new hormone synthesis. High-dose PTU also inhibits peripheral T4-to-T3 conversion.
- Step 3: Inorganic Iodine (Lugol's Iodine or SSKI): MUST be administered AT LEAST 1 HOUR AFTER thionamides. Administering iodine first provides substrate for new hormone synthesis (Wolff-Chaikoff effect requires prior organification block by thionamides).
- Step 4: Glucocorticoids (Hydrocortisone 100 mg IV q8h or Dexamethasone): Decreases peripheral T4-to-T3 conversion and treats relative adrenal insufficiency.
B. Myxedema Coma
Severe, life-threatening hypothyroid state presenting with hypothermia, severe bradycardia, hyponatremia, hypercapnia, and altered mental status. Management: IV Levothyroxine + IV Hydrocortisone (empiric hydrocortisone must be given prior to T4 to avoid precipitating acute adrenal crisis if co-existing adrenal insufficiency is present).
4. Adrenal Gland Dysfunction
A. Adrenal Insufficiency (Addison's Disease)
- Primary Adrenal Insufficiency: Destruction of all three layers of the adrenal cortex (80% autoimmune Addisonitis in developed countries; Tuberculosis is the most common cause in India). Loss of Cortisol, Aldosterone, and Androgens.
- Clinical Signs: Generalized Skin Hyperpigmentation (especially palmar creases, mucosal membranes, and surgical scars) due to elevated ACTH (POMC cleavage yields ACTH and MSH). Postural hypotension, vitiligo, weight loss.
- Electrolyte Hallmarks: Hyponatremia, Hyperkalemia, Hypercalcemia, Hypoglycemia, and non-anion gap metabolic acidosis (due to mineralocorticoid deficiency).
- Secondary Adrenal Insufficiency: Pituitary failure or chronic exogenous steroid withdrawal. Low ACTH, low Cortisol, but NORMAL Aldosterone (regulated by RAAS). No hyperpigmentation and NO hyperkalemia.
- Diagnostic Test: Cosyntropin (ACTH 250 mcg) Stimulation Test. Peak cortisol <18 mcg/dL at 30 or 60 minutes confirms adrenal insufficiency.
- Acute Adrenal Crisis Treatment: Immediate IV Normal Saline with 5% Dextrose (D5NS) + IV Hydrocortisone 100 mg bolus, followed by 100 mg q6h.
B. Cushing's Syndrome
- Clinical Presentation: Central obesity, moon facies, buffalo hump, purple cutaneous striae (>1 cm wide), proximal muscle weakness, hypertension, glucose intolerance, osteoporosis, and impaired wound healing.
- Diagnostic Algorithm (See Flowchart above):
- Screening: 24-hour Urine Free Cortisol, 1 mg Overnight Dexamethasone Suppression Test (failure to suppress morning cortisol <1.8 mcg/dL), or Late-night Salivary Cortisol.
- Plasma ACTH: Distinguishes ACTH-independent (<5 pg/mL) from ACTH-dependent (>15 pg/mL).
- High-Dose (8 mg) DST: Cortisol suppression (>50% drop) indicates Cushing's Disease (pituitary adenoma). Lack of suppression indicates Ectopic ACTH Syndrome (e.g., Small Cell Lung Cancer).
C. Pheochromocytoma
- Definition: Rare neuroendocrine tumor of chromaffin cells in the adrenal medulla secreting catecholamines (epinephrine, norepinephrine).
- The Rule of 10s: 10% Extra-adrenal (Paragangliomas), 10% Bilateral, 10% Malignant, 10% Familial (MEN 2A/2B, VHL, NF1), 10% Pediatric.
- Classic Triad: Paroxysmal Headache, Profuse Sweating (Diaphoresis), and Tachycardia, associated with severe hypertension.
- Diagnosis: Free plasma metanephrines or 24-hour urinary fractionated metanephrines and catecholamines.
UPSC CMS Perioperative Medical Management Rule: ALPHA-BLOCKADE FIRST, THEN BETA-BLOCKADE.
- Administer non-selective alpha-blockers (Phenoxybenzamine) or selective alpha-1 blockers (Doxazosin) for 10–14 days prior to surgery to control blood pressure and restore intravascular volume.
- Beta-blockers (Propranolol) are added ONLY AFTER adequate alpha-blockade to control tachycardia.
- Contraindication Warning: Starting a beta-blocker first causes unopposed alpha-1 receptor stimulation, resulting in a catastrophic, life-threatening hypertensive crisis!
A 42-year-old female diagnosed with a 3 cm right adrenal pheochromocytoma is scheduled for laparoscopic adrenalectomy. Which of the following represents the correct medical preparation sequence prior to surgery?
A 34-year-old female presents to the emergency room with severe fever (40.1°C), marked tachycardia (150 bpm, atrial fibrillation), severe agitation, and jaundice. She has a history of untreated Graves' disease. What is the correct sequence of pharmacological interventions for managing this acute condition?
A 38-year-old male presents with chronic fatigue, weight loss, dizziness upon standing, and dark hyperpigmentation of the buccal mucosa and palmar creases. Laboratory evaluation reveals sodium 128 mEq/L, potassium 5.9 mEq/L, and fasting blood glucose 62 mg/dL. Which of the following features distinguishes this primary adrenal disorder from secondary adrenal insufficiency?
A 48-year-old female with clinical Cushing's syndrome exhibits elevated 24-hour urine free cortisol. Her baseline plasma ACTH is 85 pg/mL (elevated). Following an 8 mg High-Dose Dexamethasone Suppression Test, her serum cortisol decreases from 28 mcg/dL to 6 mcg/dL (a >50% reduction). What is the underlying etiology?