Acute Thyroiditis of Actinomycosis

Abstract

N OTHERWISE HEALTHY 24-year-old man presented with progressive left neck swelling of 2‐3 weeks duration. Physical examination was remarkable for a diffusely enlarged and tender left thyroid gland with a 3 � 3 � 2 cm sized mass. The patient’s work-up revealed normal leukocyte count of 4960 cells per microliter with normal differentiation with hemoglobin of 14.2 g/dL, hematocrit of 42.8%, and platelet count of 267,000 cells per microliter. Tests of thyroid function revealed thyroxine of 4.4 � g/dL (normal, 4.5‐12 � g/dL), triiodothyronine of 0.67 ng/mL (normal, 0.6‐1.7 ng/mL), and thyrotropin (TSH) of 1.1508 � U/mL (normal, 0.4‐5 � U/mL) with antithyroglobulin antibody of below 20 (normal, below 40 IU/mL), negative antithyroid microsome antibody and TSH receptor antibody of 9.20 U/L. Thyroid scan with 99m Tc pertechnetate (Fig. 1) showed no enlarged thyroid glands with inhomogeneous decreased thyroid uptake in left lobe of thyroid gland. Thyroid ultrasonography (Fig. 2) showed an ill-defined area of heterogenous hypoechogenicity (arrows) in the left lobe of thyroid gland and left lateral neck obliterating the margin of left lobe. Precontrast-enhanced computed tomography scan of the neck (Fig. 3A) demonstrated an ill-defined low-density lesion (arrows) in the left thyroid lobe and adjacent soft tissue, lateral to left thyroid cartilage and medial to left sternocleidomastoid muscle. On contrast-enhanced scan (Fig. 3B), the lesion (arrows) was heterogeneousely enhanced with obliteration of the fat plane between the left thyroid gland. Rim-like enhancement of multiple enlarged lymph nodes along the bilateral internal jugular chains was noted. Findings are suggestive of inflammatory condition involving the left thyroid lobe and adjacent soft tissue. After the ultrasound-guided aspiration, left lobectomy of thyroid gland was performed. Histopathology (Fig. 4) demonstrated gram-positive, branching, thin, filamentous-like organisms suggestive of actinomyces, and the characteristic sulfur granules (arrows), consistent with an actinomycosis abscess of the left thyroid lobe and left lateral neck. Actinomycosis is an uncommon disease caused by Actinomyces species, gram-positive anaerobic bacteria and normal inhabitants in the oral cavity and respiratory and digestive tracts. Clinical manifestation occurs in one of three forms: cervicofacial, abdominal‐pelvic, or pulmonary actinomycosis. Cervicofacial form accounts for approximately 50% of the cases and is an exceedingly uncommon entity. Also, thyroid involvement is even more unusual. Imaging findings include an enhancing soft-tissue mass with a low-attenuating area associated with inflammation in the adjacent soft tissue including the muscles. If imaging is performed in the acute phase, actinomycosis may be seen as a localized mass with moderate homogeneous contrast enhancement (1‐3). We report a rare case of acute thyroiditis of actinomycosis with imaging findings of computed tomography (CT) and ultrasonogram.