PA31.{4,6} | Thyroid Tumors & Parathyroid Disease — Summary & Reflection

REFLECT

Take a moment to integrate what you have learned before reviewing the summary:

1. A patient presents with a 2 cm solitary thyroid nodule. The cytology report states: "Follicular neoplasm, cannot exclude malignancy (Bethesda IV)." Why can a cytologist not definitively distinguish follicular adenoma from follicular carcinoma? What additional information from histology would clinch the diagnosis of carcinoma?

2. Consider two patients with the same elevated serum calcium:
- Patient A: Outpatient, 45 years old, mild symptoms, intact PTH elevated, phosphate low
- Patient B: Inpatient, 60 years old, known lung mass, rapidly worsening hypercalcemia, intact PTH suppressed
How does the biochemistry point to the mechanism of hypercalcemia in each case? What single additional lab test would confirm Patient B's mechanism?

1. A house officer on surgical rounds says: "The patient has a brown tumor of bone — we should start chemotherapy." What is wrong with this statement, and what is the correct management?

Reflect on these before reading the summary — the answers are all in this module.

KEY TAKEAWAYS

Thyroid Neoplasms — Key Points:

• Follicular adenoma: Solitary, intact capsule, no invasion — benign; toxic adenoma causes hyperthyroidism via TSH receptor mutation
• Papillary carcinoma (80–85%): BRAF/RET/PTC; Orphan-Annie nuclei, nuclear grooves, pseudoinclusions, psammoma bodies; lymphatic spread; excellent prognosis; radioiodine-responsive
• Follicular carcinoma (10–15%): RAS/PAX8-PPARG; diagnosis requires capsular or vascular invasion on histology (not cytology); hematogenous spread (lung, bone)
• Medullary carcinoma (5–10%): From C cells; RET mutation (germline in MEN2A/2B); calcitonin + amyloid stroma; intermediate prognosis; triggers family genetic screening
• Anaplastic carcinoma (<2%): Elderly; dedifferentiation from differentiated carcinoma; markedly pleomorphic; uniformly fatal (median 3–6 months)
• Thyroid nodule approach: Ultrasound → FNAC → Bethesda classification → surgical decision

Parathyroid Disease — Key Points:

• Primary HPT: Adenoma (85%) > hyperplasia (14%, MEN1/2A) > carcinoma (<1%); PTH ↑, Ca²⁺ ↑, PO₄³⁻ ↓
• Secondary HPT: CKD most common cause; PTH ↑ compensatory, Ca²⁺ low/normal, PO₄³⁻ ↑ in CKD; all four glands enlarged
• Tertiary HPT: Autonomous PTH after prolonged secondary — post-renal transplant scenario
• Manifestations: Stones (renal), Bones (osteitis fibrosa cystica), Groans (GI), Psychic moans (CNS)
• Skeletal: Brown tumor (osteoclasts + hemosiderin, NOT a neoplasm, resolves after surgery); subperiosteal resorption of radial middle phalanx is pathognomonic radiologic sign
• Morphology: Chief cell adenoma has a rim of normal parathyroid; hyperplasia involves all four glands without a rim
• Key distinction from malignancy: Primary HPT has PTH ↑; malignancy-related hypercalcemia has PTH suppressed, PTHrP ↑