Hashimoto Thyroiditis (Chronic Autoimmune Thyroiditis)
This patient most likely has Hashimoto thyroiditis, the most common cause of hypothyroidism in the United States and the most common autoimmune disease overall. 1, 2
Clinical Reasoning
The constellation of findings points definitively to Hashimoto thyroiditis:
Diffusely enlarged, non-tender, lumpy/nodular thyroid gland - This is the classic presentation of Hashimoto disease, where lymphocytic infiltration creates a firm, irregular texture on palpation 1, 2, 3
Hypothyroid symptoms (fatigue, constipation, cold intolerance, puffy face) - These represent the most common clinical presentation, as thyroid destruction progresses to overt hypothyroidism 1, 4
Demographics - A 35-year-old woman fits the typical profile, as Hashimoto thyroiditis affects women 7-10 times more often than men and commonly presents in middle age 5, 3
Key Diagnostic Features
The pathognomonic finding is a diffusely enlarged, firm, "lumpy" or nodular thyroid gland that is non-tender. 2, 6 This distinguishes Hashimoto thyroiditis from:
- Subacute thyroiditis - Would present with anterior neck pain and tenderness 6
- Graves disease - Would cause hyperthyroid symptoms (heat intolerance, tachycardia, weight loss) rather than hypothyroid symptoms 1
- Toxic multinodular goiter - Would present with thyrotoxicosis, not hypothyroidism 1
Expected Laboratory Confirmation
To confirm the diagnosis, you should order:
- Elevated TSH with low free T4 - Confirms primary hypothyroidism 1, 4
- Anti-thyroid peroxidase (TPO) antibodies - Positive in Hashimoto thyroiditis 1, 2, 5
- Anti-thyroglobulin antibodies - Often positive but less specific than TPO antibodies 2, 7
Important Clinical Caveat
Be aware that some patients with Hashimoto thyroiditis can initially present with transient hyperthyroidism (Hashitoxicosis) due to release of preformed thyroid hormone from destroyed follicles. 6, 7, 3 However, this patient's symptoms (fatigue, constipation, cold intolerance) clearly indicate hypothyroidism, not thyrotoxicosis. The hyperthyroid phase, when it occurs, typically lasts 1-2 months before progressing to hypothyroidism, though rare cases can persist for up to 2 years. 7, 3
Management Approach
Initiate levothyroxine replacement therapy at 1.6 mcg/kg/day for overt hypothyroidism. 8, 5
- Monitor TSH levels at 6-8 weeks after starting treatment and after any dose adjustment 8
- Once stable, check TSH every 6-12 months 8
- This is typically lifelong therapy, as most patients with Hashimoto thyroiditis develop permanent hypothyroidism 1, 5, 6
Additional Considerations
Hashimoto thyroiditis carries a 1.6-fold increased risk of papillary thyroid cancer and 60-fold increased risk of thyroid lymphoma compared to the general population. 5 While imaging is not routinely indicated for diagnosis of hypothyroidism 1, if discrete nodules are palpable or develop during follow-up, thyroid ultrasound should be performed to evaluate for malignancy risk. 1