Pulmonary GGO is a very frequent and nonspecific finding in chest computed tomography [4]. Clinically, the common causes of GGO include infections (atypical bacterial and viral infections), intrapulmonary hemorrhage, diffuse alveolar damage, pulmonary embolism, bronchioloalveolar carcinoma, atypical adenomatoid hyperplasia, and active PTB [5–10]. Though the main CT signs of active PTB include bronchial spread (central lobular nodules, tree bud signs, micronodules), consolidation, voids, patch shadows with blurred edges, ground glass density shadows, and bronchial wall thickening [10], GGO can also be seen in active tuberculosis patients, and it is mainly manifested as reversed hato sign (RHS). RHS manifests as focal global GGO in the center surrounded by a continuous or discontinuous consolidation ring [10, 11]. Moreover, nodules and branching shadows can be seen in the outer ring and inner halo of tuberculosis patients with RHS, which is one of the most reliable signs to distinguish it from other lung diseases with visible reversed halo sign [12]. Nevertheless, RHS is still a rare sign type in PTB, and there is no exact data on the detection rate of RHS in PTB. PTB patients with RHS pattern tend to be relatively young, in addition, these patients usually do not have typical and milder clinical symptoms and PTB complications [13]. Meanwhile, the GGO can be also shown in hematogenously disseminated PTB. Based on the presence or absence of miliary nodules, hematogenously disseminated PTB with GGO can be divided into predominantly diffuse GGO manifestation and diffuse GGO with miliary nodules manifestation [10]. Diffuse GGO often progresses rapidly and may be misdiagnosed initially [10]. Meanwhile, diffuse GGO is mostly caused by impaired immune function, non-formation or poor formation of granuloma [10]. In PTB patients with miliary nodules, the scope of diffuse GGO is limited and miliary nodules are prominent [10]. Diffuse GGO with miliary nodules is most common in children and in adults with poor resistance, such as patients with diabetes, HIV, and a history of malignant tumors [10].
In this case, we describe an immunologically normal patient with atypical PTB symptoms in the initial stage who had chest CT imaging showing extensive and multiple GGO in both lungs with well-defined boundaries. However, the patient did not have a recent infection, intrapulmonary hemorrhage, diffuse alveolar damage, pulmonary embolism, diabetes and cancer. Conventional diagnostic methods for infectious or non-infectious causes failed to identify the etiology. Moreover, the chest CT imaging did not resemble the imaging symptoms of Mycobacterium tuberculosis infection, and the clinical manifestation is nonspecific, the diagnosis of PTB is difficult. To acquire more accurate pathogenesis, the mNGS was then applied and indicated Mycobacterium tuberculosis infection. Based on all these results, PTB was diagnosed. After effective anti-tuberculosis treatment, the GGO lesion was gradually absorbed, this radiographic evolution is rare in immune-competent PTB patient. The patient’s chest CT imaging showed extensive and multiple GGO in both lungs with well-defined boundaries. Moreover, after effective anti-tuberculosis treatment, the GGO lesion was absorbed, which was considered active inflammatory foci, therefore, the patient had active PTB in our case.
Detection of Mycobacterium tuberculosis in a patient's sputum is the gold standard for the diagnosis of tuberculosis [1]. Conventional methods, including microbial culture, microbial smear, G and GM test, M. BALF and tuberculin skin test (PPD) have low positive rate and narrow pathogen detection range, which may hinder timely treatment of PTB patients and are prone to negative effects [14]. Early diagnosis of PTB is difficult in sputum-negative patients. As an emerging pathogen diagnosis method, mNGS plays an outstanding role in the clinical diagnosis of a variety of infectious diseases, especially for infections with non-specific imaging and clinical manifestations, and repeated negative results from sputum smears and sputum cultures [2, 3]. mNGS can quickly identify multiple pathogens with unbiased, wide coverage, high efficiency, as well as assumption and minimize missed diagnosis [2, 3]. There have been many reports of Mycobacterium tuberculosis infection being diagnosed through mNGS [15, 16]. In addition, the retrospective study showed that the sensitivity of mNGS in tuberculosis diagnosis was 46%, significantly higher than that of the culture method [17]. As a result, mNGS can help clinicians improve diagnosis rates and greatly reduce the time of diagnosis. Mycobacterium tuberculosis is an intracellular pathogen, and mycobacterium tuberculosis was considered positive when at least 1 read was mapped to either the species or genus level due to the difficulty of DNA extraction and low possibility for contamination [18, 19]. Thus, in our case, 7 reads for mycobacterium tuberculosis, which can assist in the diagnosis of PTB in this patient.