The most obvious symptom of subacute thyroiditis is pain in the neck. Sometimes the pain can spread (radiate) to the jaw or ears. Painful enlargement of the thyroid gland may last for weeks or months.

Other symptoms include:

• Difficulty swallowing
• Fatigue
• Fever
• Hoarseness
• Tenderness when gentle pressure is applied to the thyroid gland (palpation)
• Weakness

Symptoms of too much thyroid hormone (hyperthyroidism) may include:

• Diarrhea
• Heat intolerance
• Nervousness
• Palpitations
• Sweating
• Tremor
• Weight loss

Later, symptoms of too little thyroid hormone (hypothyroidism) may occur, including:

• Cold intolerance
• Constipation
• Fatigue

Usually thyroid gland function returns to normal. But in some cases hypothyroidism may be permanent.

Laboratory tests early in the course of the disease may show:

• Low serum thyroid stimulating hormone (TSH) level
• High serum free T4 (thyroid hormone, thyroxine) level
• Low radioactive iodine uptake
• High serum thyroglobulin level
• High erythrocyte sedimentation rate (ESR)

Laboratory tests later in the disease may show:

• High serum TSH level
• Low serum free T4

There may be low levels of antithyroid antibodies. Thyroid gland biopsy is usually not needed, but will show a type of inflammation characteristic of this condition. Lab tests should return to normal as the condition goes away.