Amyloid 1

Question

Vignette:

A 37-year-old woman presents to her primary care physician with a one-month history of fatigue, hair loss, and dry skin. On physical examination, her heart rate is 55 bpm, and she has a delayed relaxation phase of her deep tendon reflexes. Her TSH level is significantly elevated, and her free T4 is low. A biopsy of the patient’s thyroid gland is performed, and the pathologist reports that the specimen shows a diffuse accumulation of homogeneous, eosinophilic, and acellular substance in the interstitial spaces of the thyroid gland. The material is PAS positive and shows apple-green birefringence under polarized light after staining with Congo red.

What is the most likely composition of this substance?

Choices

A. Collagen

B. Amyloid

C. Elastin

D. Fibrin

E. Hyaluronic acid

Answer

B. Amyloid

Explanation

The patient's symptoms and laboratory findings suggest hypothyroidism, most likely secondary to Hashimoto's thyroiditis. This patient's thyroid biopsy reveals deposition of amyloid, which is a common finding in long-standing Hashimoto's thyroiditis. Amyloid is an abnormal protein that can accumulate in various tissues and organs in certain diseases. It is beta-pleated sheet fibrillary protein that is essentially insoluble, leading to its deposition and disruption of normal tissue architecture. The two main types of amyloid are AL (amyloid light chain) and AA (amyloid associated). The classic histological features of amyloid are a homogeneous eosinophilic appearance on H&E stain, PAS positivity, and apple-green birefringence under polarized light after Congo red staining.