Extent of hypoechogenic area in the thyroid is related with thyroid dysfunction after subacute thyroiditis

To gain an insight into risk factors for hypothyroidism after subacute thyroiditis (SAT), we examined the correlation between initial laboratory and ultrasonographic findings and sequential thyroid dysfunction among treatment modalities.

We reviewed retrospectively the medical records of 252 patients (26 men and 226 women) with SAT who consecutively visited our thyroid clinic at Kuma Hospital for at least 6 months from 1996 through 2004.

Throughout the course, 135 patients (53.6%) developed transient or permanent hypothyroidism. Levels of TSH were most often elevated (greater than 5 IU/ml) 2 months after SAT onset regardless of treatment, and 97.0% of patients who showed transient or permanent hypothyroidism clustered within 6 months from onset. During follow-up, patients treated with prednisone (PSL) were more likely to have normal thyroid function than patients not treated or those receiving anti-inflammatory drug therapy. In patients who developed hypothyroidism with PSL treatment or without treatment, the rates of bilateral hypoechogenic areas (HEA) were 6-fold higher than those of unilateral HEA. Moreover, permanent hypothyroidism occurred in 5.9% of patients, and all patients with permanent hypothyroidism presented initially with bilateral HEA and had consequently small thyroid size with or without abnormal autoimmunity.

The rates of thyroid dysfunction after SAT were significantly lower in patients receiving PSL. Extent of HEA in the thyroid, but not laboratory findings, may be a possible marker for developing thyroid dysfunction after SAT.