What are the key clinical features that differentiate between Hashimoto's thyroiditis and subacute thyroiditis?

The key clinical features differentiating Hashimoto's thyroiditis from subacute thyroiditis primarily involve the presence of pain, the typical course of thyroid function, and specific laboratory markers [1, 2, (Synoracki et al., 2016)].

Subacute thyroiditis (also known as De Quervain's thyroiditis) is characterised by a **painful and tender thyroid gland**, which is a hallmark differentiating feature [1, (Synoracki et al., 2016)]. This pain can often radiate to the jaw, ear, or chest ¹. Its onset is typically acute or subacute, often following a viral illness, and patients may also experience fever, malaise, and myalgia [1, (Synoracki et al., 2016)]. Thyroid function in subacute thyroiditis commonly follows a triphasic course: an initial hyperthyroid phase due to the release of preformed hormones, followed by a transient hypothyroid phase, and usually culminating in a return to euthyroidism [1, (Synoracki et al., 2016)]. Laboratory tests typically show markedly elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), while thyroid antibodies are usually negative or present at low titres [1, (Synoracki et al., 2016)]. The condition is generally self-limiting, resolving within months [1, (Synoracki et al., 2016)].

In contrast, Hashimoto's thyroiditis is typically a **painless condition** ². It is an autoimmune disorder with a gradual onset, often presenting with symptoms of hypothyroidism such as fatigue, weight gain, and cold intolerance ². While a goitre may be present, it is usually firm and non-tender ². Hashimoto's thyroiditis primarily leads to chronic hypothyroidism, although a transient hyperthyroid phase (Hashitoxicosis) can occur ². The presence of high titres of thyroid peroxidase (TPO) antibodies and/or thyroglobulin antibodies is characteristic of Hashimoto's thyroiditis ². Inflammatory markers like ESR and CRP are not typically elevated to the same extent as in subacute thyroiditis ¹,².