The above described findings are impressive of chronic lymphocytic (Hashimoto) thyroiditis (in the clinical setting of hypothyroidism).
Hashimoto thyroiditis is a chronic lymphocytic / autoimmune thyroiditis. Patients can demonstrate mild transient hyperthroidism, followed by euthyroidism & finally fibrosis ensues and typically the patient is hypothyroid (thyroid replacement therapy is indicated). Ultrasound shows an enlarged lobulated heterogeneous gland with a myriad of tiny hypoechoic nodules, fibrosis occurs in the late stages with dense echogenic fibrous septa. Thyroid scintigraphy shows decreased uptake. Hashimoto thyroidits can be complicated by thyroid lymphoma.
The differential diagnosis is:
- primary thyrotoxicosis (Graves disease): the gland is diffusely and homogeneously enlarged. The patient is hyperthyroid. Thyroid scintigraphy shows diffuse homogeneously increased uptake. Early Hashimoto thyroiditis may mimic primary thyrotoxicosis (the gland is enlarged with increased vascularity and increased uptake at scintigraphy); however the patient is usually euthyroid in early Hashimoto thyroiditis.
- secondary thyrotoxicosis (Plummer's disease): Enlarged heterogeneous gland with patchy areas of increased vascularity. Toxic nodules show increased vascularity and increased uptake at thyroid scintigraphy with inhibition of the uptake of the rest of the gland.
- subacute granulomatous (De Quervain) thyroiditis: PAINFUL thyroiditis; usually post-viral. Patients initially presents with hyperthroidism due to release of thyroid hormones into the circulation by the destroyed thyroid follicles, followed after 2-4 months by hypothyroidism due to depleted follicles. Finally, after 2 months, the patient return to the euthyroid state. The gland appears mildly enlarged and slightly hypoechoic with increased vascularity. Thyroid scintigraphy shows decreased uptake.
- subacute lymphocytic thyroiditis: PAINLESS thyroiditis; usually in young women and may be post-partum. Minimally enlarged gland with hyperthyroidism that returns to normal euthyroid state
- Riedel thyroidtis is a differential of fibrosing Hashimoto thyroiditis