Histological sections of a medullary thyroid carcinoma show nests of spindle-shaped cells separated by deposits of an amorphous eosinophilic hyaline material. This material stains positively with Congo red and shows apple-green birefringence under polarized light. The protein deposited is:

• A Immunoglobulin light chains
• B Transthyretin produced by the liver
• C Procalcitonin-derived peptides secreted by the neoplastic C cells ✓
• D Amyloid A derived from chronic inflammation

Explanation

Medullary thyroid carcinoma produces calcitonin and related prohormone peptides, and cleavage products of procalcitonin deposit as amyloid in the stroma in a variable proportion of cases. Light chain amyloid occurs in plasma cell dyscrasias, AA amyloid follows chronic inflammatory states, and transthyretin causes familial ATTR neuropathies, none of which apply here. Calcitonin itself can be demonstrated in the amyloid by immunohistochemistry.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.