Symptoms of thyroiditis may differ, depending upon how the disease affects the thyroid gland.

In many cases, thyroiditis causes the thyroid gland to become underproductive, producing fewer hormones than the body requires, leading to hypothyroidism. Symptoms of hypothyroidism may include:

• Fatigue and sluggishness
• Enlarged thyroid gland (goiter)
• Puffiness of the face and ankles (due to edema)
• Increased sensitivity to cold
• Depression or other personality changes
• Forgetfulness
• Unexplained weight gain
• Constipation
• Muscle aches or muscle cramps

In some cases, thyroiditis may cause symptoms that mimic hyperthyroidism. This occurs when additional thyroid hormones leak out of the thyroid gland and into the bloodstream, causing thyrotoxicosis (high levels of thyroid hormones in the blood). These symptoms may include:

• Anxiety
• Enlarged thyroid gland (goiter)
• Irregular or rapid heartbeat
• Irritability
• Sudden, unexplained weight loss
• Insomnia
• Increased sweating and intolerance to heat
• Tremor

Throat pain, often in only one side of the neck, is an additional symptom that is typically present in subacute thyroiditis. Symptoms of hoarseness, coughing, difficulty swallowing (dysphagia) and difficulty breathing (dyspnea) may also appear in Riedel's thyroiditis.