Introduction

Thyroid involvement by disseminated tuberculosis is rare, and primary involvement of this organ is rarer, even in countries with a high incidence of tuberculosis¹. Approximately 5 cases have been reported in Europe in the last 10 years, all of them of patients from South American or Asian countries with a higher incidence of tuberculosis than in Europe. We present the case of a Spanish patient with an isolated thyroid nodule.

Clinical Case

The patient is a 50 year old woman with no medical history of interest. As the only important antecedent, she works in a health center performing Mantoux tests. She was evaluated by her primary care physician for presenting a left cervical nodule. An ultrasound was performed which showed a lesion with irregular borders and solid appearance covering a large part of the middle and lower third of the left thyroid lobe. Its major axis measured approximately 3 cm and showed signs of an infiltrative lesion (Fig.1). No pathological adenopathies were observed. In view of this finding, the lesion was punctured, resulting in a follicular lesion of undetermined significance, Bethesda III. With these results, the patient was referred to the general surgery service where a left hemihyroidectomy was proposed, with the possibility of needing to complete the thyroidectomy depending on the results.

Figure 1 Preoperative ultrasound showing a heterogeneous nodule of approximately 3 cm in the left thyroid lobe. 

As planned, a programmed left thyroidectomy was performed. During surgery, no significant alterations were observed on the surface of the left thyroid lobe. The described nodule was palpable but showed no signs of infiltration of adjacent structures.

Intraoperative study of the specimen was not performed because there were no macroscopic signs of malignancy. The patient had no postoperative complications and was discharged the same day. The pathological analysis of the surgical specimen showed a granulomatous thyroiditis with non-necrotizing epithelial granulomas with the presence of multinucleated giant cells. In view of the possibility of an infectious etiology, more stains were performed, evidencing acid fast bacilli using the Ziehl-Nielsen technique. This finding confirmed the tuberculous origin of the patient's nodule (Fig. 2).

Figure 2 Tuberculous bacilli stained by ziehl neelsen technique in thyroid parenchyma. 

The patient was studied by the department of infectious diseases where complementary tests were performed excluding affectation at other levels. Also, quadruple antituberculosis therapy was initiated with isoniazid, rifampicin, pyrazinamide, and ethambutol.

Discussion

The thyroid gland has a high intrinsic resistance to infections as well as to metastatic involvement. This is probably due to the high blood flow, the high concentration of iodine and oxygen and the possible bacteriostatic effect of thyroid hormones²,³. Therefore, thyroid involvement by tuberculosis is extremely rare.

Hematogenous or lymphatic spread in the context of a miliary disease is responsible for most cases, with thyroid involvement of about 14%⁴. Primary thyroid tuberculosis is an even rarer process and is difficult to diagnose. Women are affected more frequently and in most cases the patients are euthyroid. The clinical presentation is very variable, the most frequent is a solitary nodule, but it can present as a fast growing goiter or a thyroid abscess. Sometimes, it can appear with dyspnea or dysphagia due to the involvement of adjacent structures⁵.

Cervical ultrasound, although necessary, is often non-specific, as are CT and MRI scans. Fine needle biopsy of lesions can be very useful. The visualization of granulomas with case necrosis is sufficient to assume that it is a tuberculous thyroiditis. Similarly, culture of tuberculosis in material obtained by fine needle biopsy or visualization of acid fast bacilli would confirm the diagnosis⁶. In the presence of suspicious granulomas and negative cultures, a PCR for tuberculosis of thyroid tissue can be performed. A positive result would support the diagnosis.

However, on many occasions, such as in our patient, fine needle biopsy is non-specific. Intraoperative pathological study can be useful and cost effective in these cases with suspected malignancy in the ultrasound and inconclusive biopsy⁷. However, in this particular case this option was not considered because of the absence of suspicious findings during surgery.

Usually, the definitive diagnosis is given by the study of the surgical specimen. The presence of caseous granulomas, a positive stain, a tuberculosis culture or a positive PCR would give us the diagnosis.

Medical treatment with anti-tuberculosis agents according to local resistances is the main treatment and can avoid surgery if the diagnosis is made by fine needle biopsy⁸. In case of acute abscesses, surgical drainage may be necessary.

In conclusion, thyroid tuberculosis is a rare entity with a highly variable presentation and a complex diagnosis when it is not suspected. It usually occurs in patients with disseminated tuberculosis who are from endemic countries. However, sometimes, as in our patient, it may present as a solitary nodule in a patient with no history of previous tuberculosis and no contact with areas of high prevalence. Therefore, at the minimum suspicion, it is necessary to consider this option to perform the necessary complementary studies for its diagnosis.