**3.4 Subacute (DeQuervain's) thyroiditis**

It is a nonsuppurative thyroiditis caused by viral infection or as a result of post-viral illness. In twin study, some link of genetic association was also found [26]. Subacute thyroiditis is characterized by neck pain and tenderness. Initially disease presents with fever, fatigue, and myalgia along with hyperthyroidism that is followed by euthyroidism and then hypothyroidism, and lastly euthyroidism is achieved. A less or absent uptake is seen by radionuclide uptake study. Color Doppler study reveals low blood flow in the hyperthyroid phase which normalizes once euthyroidism is achieved. On laboratory study TSH remains suppressed, and free T4 and free T3 are raised during the hyperthyroid phase.
