Introduction

Tuberculosis affecting the thyroid gland is a rare condition, even in countries with a high prevalence of this disease. The exact figures for its incidence are unavailable; however, in different studies, it has been found to be ranging from 0.4% [₁] to 1.15% [₂] of all thyroid lesions.

Case Report

A 40 year old male patient presented with slow, progressively increasing swelling over right side of midline of neck, since 6 months. There were occasional episodes of scanty, whitish discharge from the swelling. On examination, there was a 7.0 x 5.0 cm swelling on right side of midline of neck, which moved well with deglutition, but not on protrusion of tongue. The swelling had a smooth surface, with firm to hard consistency, and ill-defined margins. A small sinus opening with little whitish discharge was present in the center of the swelling. The rest of the thyroid gland was normal. No symptoms of complications, or hypo or hyperthyroidism were present. There was no previous history of tuberculosis or contact with an open case of tuberculosis.

Investigations revealed a normal haemogram except a raised ESR of 50mm. T3, T4, TSH levels were normal. A chest X-ray was also normal. A fine needle aspirate of the swelling showed only few degenerated cells in a haemorrhagic background. Smears of the discharge from sinus showed only necrotic debris and were inconclusive.

The patient underwent right hemithyroidectomy and he made an uneventful postoperative recovery. Gross examination of the specimen showed a single globular mass measuring 7.0 x 6.0 x 4.5 cm. The outer surface was shiny with areas of congestion. On cut section, a single large cavity was seen, measuring 6.0 x 4.5 cm, with a maximum wall thickness of 1.8 cm, and containing friable necrotic material. A smear as well as culture swab from necrotic material were sent for bacteriological examination.

Microscopic examination of multiple sections from the thyroid swelling showed atrophic thyroid follicles with lymphoid aggregates in the stroma (Fig. 1), large areas of haemorrhage, fibrosis, calcification, and areas of caseous necrosis surrounded by epithelioid cells and Langhan's giant cells (Fig. 2). Sections from the wall of abscess cavity revealed caseous necrosis with epithelioid histiocytes (Fig. 3) and fibrosis. A histopathological diagnosis of granulomatous thyroiditis favouring tuberculosis was given. The smears as well as culture from necrotic material showed tubercule bacilli, thus confirming the diagnosis.

Figure 1

Figure 1: Photomicrograph from thyroid swelling showing atrophic thyroid follicles with lymphocytic infiltrate in stroma, along with formation of lymphoid aggregates (H & E, x50).

Figure 2

Figure 2: Photomicrograph showing epithelioid cell granuloma with Langhan's giant cell ( < ), and lymphocytic infiltrate (H & E, x 125).

Figure 3

Figure 3: Photomicrograph from thyroid abscess wall showing caseous necrosis, epithelioid histiocytes ( > ), calcifications ( ), and fibrosis (H & E, x 50).

The patient was placed on isoniazid, rifampicin, ethambutol, pyrazinamide along with pyndoxme and diclofenac. Follow-up over three months after operation was uneventful.

Discussion

It is observed that certain tissues are relatively resistant to tuberculous infection, and so it is rare to find tubercles in heart, striated muscle, thyroid and pancreas [₃]. The relative immunity of thyroid gland has been confirmed but has not been explained. Primary involvement of thyroid gland is difficult to explain. A latent focus of infection perhaps is of great importance in the development of such type of extrapulmonary tuberculosis [₄]. This is in contrast to the thyroid involvement associated with pulmonary or extrapulmonary tuberculosis, where spread of disease occurs by hematogenous or lymphogenous route, or directly from larynx or tubercular cervical lymphadenitis [₅]. Miliary spread to thyroid gland as a part of generalized dissemination has never been shown to give rise to clinical thyroid disease. Alternatively, focal caseous tuberculosis of thyroid may present as localized swelling mimicking carcinoma, as a nodule, lump, cold abscess or rarely an acute abscess [₆]. Only an occasional case of cold abscess presenting with a chronic sinus is reported in the literature [₇].

The symptoms of thyroid tuberculosis are misleading, and pathological findings are of increasing importance for diagnosis. Fine needle aspiration has proved quite efficient in detecting tuberculosis of thyroid gland [₂]. The following pre-requisite conditions for diagnosis of thyroid tuberculosis were described in early 1939: 1) demonstration of acid fast bacilli within thyroid, 2) a necrotic or abscessed gland, 3) demonstration of tuberculous focus outside. Histological and bacteriological confirmation is adequate and fulfillment of third criterion is not essential [₅]. Nowadays it is stated that acid fast bacilli are not always found, and therefore multiple coalesced and caseated epithelioid cell granulomas along with giant cells are considered to be diagnostic of tuberculous affection of the gland [₈].

The important differential diagnoses are thyroid cancer, acute thyroiditis, Riedel thyroiditis and thyroid nodules. Lymphocytic infiltration and presence of granulomas may also be seen in sarcoidosis, subacute thyroiditis and goitrous autoimmune thyroiditis [₆].

Antitubercular therapy and surgical removal of the affected parts of the thyroid gland are the most common methods of treatment. Repeated puncture drainage in combination with antitubercular drugs is applied nowadays as well [₆].

Acknowledgments