Diagnosis: Hashimoto's Thyroiditis (Autoimmune Hypothyroidism)
The most likely diagnosis is Hashimoto's thyroiditis, which presents with a nodular/lumpy thyroid gland (goiter), facial puffiness (myxedema), and hypothyroid symptoms, and should be confirmed with TSH, free T4, and anti-thyroid peroxidase antibodies. 1, 2
Diagnostic Workup Algorithm
Initial laboratory testing should include:
- Serum TSH (will be elevated >4.5 mIU/L in overt hypothyroidism) 3
- Free T4 (will be low in overt hypothyroidism) 3
- Anti-thyroid peroxidase (anti-TPO) antibodies (elevated in Hashimoto's thyroiditis) 1, 2
- Anti-thyroglobulin antibodies (often elevated in Hashimoto's) 2
Imaging approach based on TSH results:
- If TSH is elevated (hypothyroid): Thyroid ultrasound is the appropriate first-line imaging to characterize the nodular thyroid 4
- Ultrasound will typically show diffuse hypoechogenicity (reduced echogenicity) and heterogeneous echotexture in Hashimoto's thyroiditis 2
- Radionuclide scanning is NOT indicated for hypothyroidism workup, as it does not differentiate among causes of hypothyroidism 4
Clinical Features Supporting This Diagnosis
Classic presentation includes:
- Nodular or diffuse goiter (lumpy thyroid) that is typically nontender 1, 2
- Puffy face (myxedema) representing fluid accumulation in subcutaneous tissues 3
- Hypothyroid symptoms: fatigue, cold intolerance, weight gain, hair loss, constipation 3
- Predominantly affects women 2
Hashimoto's thyroiditis is the most common cause of hypothyroidism in iodine-sufficient areas and the most common autoimmune disease. 2
Critical Diagnostic Pitfall to Avoid
Do not proceed directly to thyroid scintigraphy (uptake scan) in a patient with elevated TSH and hypothyroid symptoms. 4 Radionuclide scanning wastes resources and provides no diagnostic value in hypothyroidism, as all causes show decreased radioiodine uptake. 4 The scan is only indicated when TSH is LOW (suppressed), not elevated. 4
Treatment Initiation
Once overt hypothyroidism is confirmed (elevated TSH with low free T4), initiate levothyroxine replacement therapy:
- Starting dose in adults: 1.6 mcg/kg/day for new-onset hypothyroidism 5
- Monitor TSH levels 6-8 weeks after starting therapy and after any dose adjustment 5
- Target: normalize serum TSH to within reference range 5
- Treatment is typically lifelong for Hashimoto's thyroiditis 1
Role of Ultrasound in This Patient
Thyroid ultrasound serves multiple purposes beyond diagnosis:
- Characterizes the nodular components to assess malignancy risk using standardized risk stratification systems 4
- Identifies which nodules may require fine-needle aspiration biopsy based on suspicious ultrasound features 4
- Establishes baseline thyroid size and nodule characteristics for future monitoring 4
The combination of elevated anti-TPO antibodies, reduced thyroid echogenicity on ultrasound, and appropriate clinical features establishes the diagnosis of Hashimoto's thyroiditis without need for biopsy in most cases. 2
Special Consideration: Hashitoxicosis
In rare cases, Hashimoto's thyroiditis can present with initial hyperthyroid symptoms (Hashitoxicosis) due to release of preformed thyroid hormone from damaged follicles, followed by eventual hypothyroidism. 6, 2 However, the presence of hypothyroid symptoms and puffy face in this patient indicates the hypothyroid phase, making this variant unlikely.