Unmasking Pott Disease: A Diagnostic Challenge Mimicking Metastatic Lung Cancer – A Case Report

Introduction

Tuberculosis (TB) is a disease caused by acid-resistant bacilli from the group Mycobacterium tuberculosis complex, which were discovered and described by Robert Koch in 1882 [1]. TB is one of the oldest infectious diseases and remains among the 10 top causes of death worldwide [2]. The factors that predispose an individual to contracting TB include poverty, undernourishment, alcohol dependence, drug abuse, immunosuppressive therapy, and HIV infection [3–6]. It is estimated that over 2 billion people globally are infected with M. tuberculosis, and approximately 10 million new infections are recorded each year. There are also estimates that 1.6 million people die of TB every year [7,8]. Poland belongs to the countries with a low incidence of tuberculosis (11.4 cases per 100 000 people in 2023) [9–11]. According to the latest data from Polish sanitary and epidemiological stations issued annually in a report collated by the Institute of Tuberculosis and Lung Diseases, there were 4314 cases of TB in total, including 3787 new cases, in 2022. The most common form was tuberculosis of the lungs, which constituted 96.2% of all cases [11]. There were also 4 diagnosed cases of tuberculosis of the spine [11].

Tuberculosis of the bones and joints now corresponds to 2.2% to 4.7% of all cases of TB in Europe and the United States [12]. Involvement of the bones and joints accounts for about 10% of extrapulmonary tuberculosis cases, and the most commonly affected site is the spine, accounting for 50% to 70% [13–15]. Tuberculosis spondylitis is one of the oldest diseases plaguing humans. It has been detected in Egyptian mummies dating back to 3400 BC [16]. The damage to the disc space and adjacent vertebral bodies as well as to other elements of the spine with progressing kyphosis has been named Pott disease [17]. The disease manifests as chronic backache, which typically locates in the lower thoracic and lumbar spine. The infection begins as inflammation of the intervertebral discs and then progresses along the ligaments of the vertebral column, invading adjacent vertebral bodies [18].

The aim of this paper is to present a case of a patient with an insidious picture of extrapulmonary tuberculosis implicating disseminated neoplastic disease.

Case Report

A 69-year-old male patient, with a history of hypothyroidism, prostatic hypertrophy, a former smoker (not smoking for 26 years), was admitted to the Pulmonology Department of the hospital on February 28, 2023, presenting with chest pain that had been worsening for about 3 weeks, pyrexia, dry cough, and loss of appetite (loss of body mass by about 10 kg in 3 months). He was a professional teacher who had fallen ill after having resided in Venezuela for an extended period. He had relocated to Poland 2 years earlier and denied any history of tuberculosis exposure. A chest X-ray taken in an outpatient clinic prior to the admission to hospital demonstrated the widening of a shadow of the left pulmonary hilum (Figure 1). A computed tomography (CT) scan of the chest, performed on March 1, 2023, revealed an infiltrate mass in the hilum of the left lung, adjacent to the left pulmonary artery (Figure 2). A pathological 20-mm wide lymph node was visualized in the subcarinal region, a lymph node, measuring 15-mm wide, was seen in the right hilum, and a lymph node with a diameter of 16 mm located below the left lower pulmonary veins (Figure 3). At the height of the C6-C7 vertebrae, there was a visible pathological mass, heterogenous and weakly separated, 33 to 38 mm in dimension, destroying the antero-right parts of the vertebral bodies, the right arch of C6, and invading the prespinal tissues on the right side. It was adjacent to the right side of the esophageal wall and spreading down the spine toward Th2, probably pervading from the front into the spinal canal (Figure 4). The lesion was assessed on magnetic resonance imaging, where the image indicated metastasized neoplastic disease. During bronchofiberoscopy, performed on March 2, 2023, specimens were taken from the submucosal infiltrate underneath the departure of segment 6 of the left lung, and their histopathological examination did not reveal any neoplastic tissue. A bronchial secretion test for specific infection, acid-fast bacilli, yielded a negative result. Histopathological examination of sections from the nodular infiltration on the lateral wall of the bronchi revealed tissue fragments partially covered with epithelium, consisting of fibrous connective tissue, T and B lymphocytes, plasma cells, and neutrophils. Additionally, the bronchial secretions predominantly contained cuticles of normotypic respiratory epithelium, squamous epithelium, macrophages, and lymphocytes. On March 9–14, 2023, the C4-Th2 area was irradiated (20 Gy in 5 fractions). Due to the newly diagnosed paresis of the right peroneal nerve, a CT scan of the entire spine was done, which revealed a hypodense infiltrate in the projection of the external obturator muscle and the quadratus femoris to the right side, and within the adductor magnus muscle, occupying an area of approximately 67×22 mm, with no evident pathological enhancements.

The follow-up chest CT scan on March 29, 2023, preceding the patient’s qualification for an endobronchial ultrasound (EBUS) test, revealed significant regression of the tumor nodal mass (Figure 5). On March 20, 2023, an EBUS and endoscopic ultrasound (EUS) needle aspiration test was conducted, in which samples of material from a group 7 lymph nodes and from the tumor mass in the proximity of C6-C7 were collected for cytological examination. Again, no neoplastic tissue was detected. Histopathological examination revealed bronchial epithelial cells, macrophages, and lymphoid cells. On April 6, 2023, the patient was qualified for an open biopsy of the C6 and C7 vertebrae, which was performed at the Orthopedic Ward of the MSWiA Hospital in Olsztyn. The histopathological examination revealed chronic granulomatous inflammation, with the presence of necrosis. No cultures were performed. On May 2, 2023, the final results were obtained from the culture of bronchial secretion grown on the Löwenstein-Jensen medium. The strain of M. tuberculosis complex, with full drug sensitivity, was identified. The patient was referred to the Tuberculosis Ward, where his treatment was undertaken in line with the relevant standards. Anti-tuberculous treatment was complicated by an abscess in the scrotal area. Genetic and culture results (DNA Mtbc BD MAX, MGIT) confirmed tuberculosis. No other treatment complications were observed.

Discussion

We reported a case of a 69-year-old patient with Pott disease, whose signs and symptoms were initially considered to display an image of disseminated neoplastic disease with a probable origin in the lungs. Changes in the spine were thought to be metastases of the primary lung cancer. Due to the CT image, with the visible invagination of the pathological mass at the C6-C7 vertebrae, prior to the final diagnosis and for fear of tetraplegia, the patient was submitted to radiotherapy of this area.

In 2022, 4 cases of tuberculosis spondylitis were detected in Poland; meanwhile, approximately 20 000 new cases of lung cancer are diagnosed in our country each year [11,19]. The differential diagnosis of this type of lesion in the spine includes bacterial infections (eg, brucellosis), neoplastic diseases, myeloma, or dissemination of neoplastic disease [20–22]. An unquestionable problem in the present case was the co-occurrence of the tumor nodular mass on the chest CT scan, which in the early clinical picture implicated the diagnosis of disseminated cancer. However, this diagnosis was undermined by the regression of the lesion observed later in the follow-up chest CT and by the results of the 2 biopsies (during bronchofiberoscopy and during the EBUS test), which did not reveal any changes of the neoplastic character.

The invasion of the spine in a course of TB is usually a consequence of the spread of M. tuberculosis via blood to the vascular system of the spongy bone of the vertebral bodies [21,23]. The primary site of infection is a lesion in the lungs or an infection of the genitourinary system. Approximately 50% of cases are diagnosed as concomitant lung lesions, but active pulmonary tuberculosis is rarely confirmed [12,24].

Initial suspicion of Pott disease is often based on the clinical picture and results of imaging tests, but the final diagnosis relies on the isolation and identification of the pathogen. This applies to all pulmonary and extrapulmonary forms of tuberculosis [25,26].

Conventional microbiological methods, such as staining with the Ziehl-Neelsen method for acid-resistant bacilli and culture of M. tuberculosis on the Löwenstein Jensen medium, have low sensitivity and specificity. Another problem is that culturing of M. tuberculosis is time-consuming and takes from 6 to 8 weeks [27]. However, culture methods can identify far fewer tuberculosis rods (10–100/mL of sample) spotted under a microscope and they enable the identification of M. tuberculosis as well as the determination of its sensitivity to drugs, which makes them criterion standard in the diagnosis of TB. In the present case, the screening test for TB (acid-fast bacilli) gave a negative result, whereas the culture method confirmed the presence of M. tuberculosis. The nucleic acid amplification test (NAAT) serves as a rapid alternative to conventional bacteriological diagnostics, primarily by reducing diagnostic time. NAAT detects M. tuberculosis ribosomal RNA or DNA directly from sputum specimens, regardless of acid-fast bacilli smear results, whether positive or negative [28]. An added advantage is its capability to assess drug sensitivity. Despite clinical suspicions of disseminated cancer, the patient underwent a mycobacteria growth indicator tube test, with subsequent confirmation of acid-fast bacilli in the culture after several weeks. The delay in performing a rapid nucleic acid test contributed to the prolonged diagnostic process.

The time waiting for the results of a bacterial culture was of fundamental importance in the present case. The etiological confirmation of a diagnosis can be achieved either by determining the presence of acid-resistant bacilli in the pathological material or by confirming the presence of epithelial cells in a histopathological test on biopsy material [29]. Needle biopsy of a lesion is the criterion standard in the early histopathological diagnosis of spinal tuberculosis [30]. Histological examinations confirm the diagnosis of tuberculosis spondylitis in about 60% of patients. The cytological changes most often observed are epithelial cell granulomas (90%), granular necrotic background (86%), and lymphocytic infiltration (76%). In over 50% of patients, the biopsy material is found to contain disseminated multinucleated cells and Langhans giant cells [21,31,32]. In our patient, the biopsy revealed granulomatous inflammation with the presence of necrosis, which is typical of tuberculosis [33]. Despite the absence of specific diagnostic criteria, the patient’s clinical presentation with respiratory and osteoarticular symptoms, coupled with a history of extended residence in a high TB-burden area, such as Venezuela, should have triggered a robust suspicion of TB. The biopsy findings of granulomatous inflammation with necrosis further supported this suspicion, aligning with typical features of tuberculosis spondylitis. This case underscores the need for a proactive approach to diagnosis, where clinical judgment is used to initiate empiric TB treatment promptly in cases of high suspicion, even before microbiologic confirmation is obtained. Waiting for definitive test results can result in diagnostic inertia and potential harm to the patient’s health. Therefore, healthcare providers should leverage available clinical evidence and diagnostic tools, such as histopathological examinations and rapid molecular tests, to expedite treatment initiation and improve patient outcomes in suspected cases of tuberculosis.

Conclusions

The presented case highlights the key role of making a differential diagnosis correctly, employing all available methods. The lack of specific clinical criteria for the diagnostic process should not dissuade us from searching for tuberculosis, despite a suggestive clinical image. Even in countries with low tuberculosis incidence, patients presenting with lung or spinal lesions should be evaluated for tuberculosis. The utilization of readily accessible rapid molecular tests substantially reduces the duration of tuberculosis diagnosis. It is imperative to ensure that an appropriate diagnostic approach has been undertaken. Rapid molecular tests, which are increasingly accessible, can substantially shorten the time to diagnosis and should be integrated into diagnostic algorithms to expedite treatment initiation and improve patient outcomes, particularly in cases of suspected tuberculosis.