The thyroid is an organ resistant to infections due to its encapsulated position that protects it from the outside, high vascularization, lymphatic drainage, high concentration of tissue iodine and production of hydrogen peroxide for the synthesis of thyroid hormone [4]. The above explains why infectious thyroiditis is infrequent. The exact incidence is unknown, but it is estimated to correspond to 0.1 to 0.7% of thyroid diseases [6].
Suppurative thyroiditis (ST), develops in patients with pre-existing risk factors, especially immunosuppression states and on a thyroid that may be previously healthy, as demonstrated in the series of Lafontaine et al., published in 2021, in which 200 cases of ST were collected between 2000 and 2020 and in which only 20% of the 130 patients who had bacterial ST had pre-existing thyroid disease [4, 7].
Clinically, thyroiditis manifests with pain (89–100%), fever (82–92%), dysphagia (46–91%), erythema (38–82%) and dysphonia (15–82%) as main symptoms [7, 8]. In the case presented, the patient presented pain as the only symptom associated with thyroiditis. Within the laboratory findings, there are no specific paraclinical findings to guide towards a possible ST, as any infection can present with elevation of acute phase reactants and the thyroid profile can be variable, Yu et al. published a series of 191 cases reported between 1980 and 1997 in which 68% of the patients were euthyroid [9], however, the most recent meta-analysis by Lafontaine found that 42% of bacterial ST (BST) and 40% of fungal ST (FST) had hyperthyroidism at presentation and that at least 36% of BST cases had free T4 more than twice the upper limit of normal. In the long term 21% of the BST and 50% of the FST developed hypothyroidism, which makes it difficult, only by thyroid tests, to differentiate between ST and subacute thyroiditis (SAT) [7]. Our patient did not have a TSH measurement during the course of thyroiditis.
Nothing different occurs with imaging studies. Both ultrasound and tomography can be very non-specific in the early stages, since abscess formation can be observed in acute inflammation and thyroid scintigraphy is usually abnormal, with evidence of cold nodules [10, 11]. This is why fine-needle aspiration (FNA) is preferred as the method of choice for the diagnosis of ST, since it allows not only the collection of microbiological samples, but also the performance of therapeutic drainage and differentiation with SAT in cases of thyrotoxic presentation [4, 12].
Regarding etiology, in the 3 large series we have so far, infection by Gram-positive bacteria, mainly Streptococcus spp. (9–16%) and Staphylococcus spp. (9.5–15%), occurred more frequently, while Nocardia spp. was documented in only 6 patients in the 3 series, representing 4% in the largest series. Among the Gram-negative microorganisms, Salmonella was the most frequently isolated microorganism. M. tuberculosis had a prevalence between 9.3–16%; it is noteworthy that 11% of the STs in Lafontaine's series were polymicrobial [7–9].
Regarding infection by Nocardia, it is known that in 60% of cases there is a pre-existing compromise of the immune system and that having received high doses of prednisone has an odds ratio (OR) of 26 for infection [13, 14].
The clinical presentation is variable, there may be involvement limited to the skin, pulmonary involvement occurs in 73% of patients with subacute or chronic symptoms, characterized by cough, dyspnea, hemoptysis and fever. Abscess formation and cavitary disease may occur, in some cases endobronchial masses and empyema [15, 16]. In the case of central nervous system (CNS) involvement, this manifests as granulomas or abscesses, which in 50% of the cases are multiple and it is known that when there is CNS involvement in 80% of the cases, the patients are immunosuppressed, and this will define prognosis since an immunosuppressed patient with nocardiosis in the CNS has a mortality of 55% [17–19]. In rarer cases there may be keratitis or bacteremia and disseminated presentation characterized by the formation of generalized abscess foci in 2 or more sites is not uncommon [20].
Regarding ST by Nocardia spp., so far we have a series published in 2021 by Esnault et al., of 11 cases documented since 1978, in which all patients were immunosuppressed, 10 of them had disseminated infection, 7 had infection by N. asteroides, 2 by N. farcinica, 1 by N. brasiliensis and 1 by N. abscessus, all with variable clinical presentation, from asymptomatic course, presence of painful cervical nodules, to painful thyromegaly, with dysphagia, dysphonia and thyrotoxicosis [21].
Diagnosis can be difficult, because although it can grow in usual culture media, its best performance is in selective culture media; it requires an incubation time of up to 14 days and molecular tests such as PCR have a specificity of only 74% and do not differentiate infection or colonization [15, 22]. In the case presented, isolation of Nocardia was only achieved in the thyroid; it should be noted that the patient had previously taken amoxicillin/clavulanate, which is active against some species of Nocardia, which could have altered the performance of the cultures.
Mycobacterium tuberculosis is a recognized pathogen in patients with immunosuppression; however, infections in the thyroid gland are infrequent, even in areas where it is endemic, it is estimated to occur with a frequency of 0.1–0.4% of all cases of TB. There are few case reports and series of tuberculous thyroiditis, where a predominance in the female sex is reported with a range between 14–83 years and a mean age of 43 + 17 years for women. Its range of presentation is varied as solitary nodule, diffuse or multinodular goiter [23, 24].
Regarding the coinfection of Nocardia and tuberculosis, this is the first case reported in the literature, it is an infrequent pathology, due to uncommon germs that coincided in a host with multiple risk factors for infection by both microorganisms, with an unfavorable prognosis.