Lung Adenocarcinoma with Miliary Metastases and Left Femur Pathologic Fracture: an Unusual Case Mimicking Disseminated Tuberculosis

Abstract

Lung adenocarcinoma can have a varied appearance at presentation. Solid, ground-glass, or part-solid and part-ground-glass nodules are commonly seen [1]. Multifocal areas of consolidation that are peribronchovascular and contain air bronchograms may also be identified [3]. Multiple discrete nodules, or the so-called miliary pattern, are rare, with few cases reported in the literature [3, 10, 12, 14]. This pattern is more commonly reported as multifocal or diffuse adenocarcinoma, and detailed data regarding the incidence has not yet been studied in depth. However, in one case report of 73 patients with adenocarcinoma, 14 presented with multifocal disease, though only one had innumerable discrete nodules [19, 22]. In another study examining 548 patients with non-small cell lung cancer, 504 patients presented with a dominant lesion (stage I disease) and 44 with multifocal disease. Of the 44 patients, 18 had multifocal adenocarcinoma [2]. Some have suggested that the miliary pattern of adenocarcinoma may be produced by bone or liver metastases that continually seed the lung, though this has yet to be verified [10]. Because the miliary pattern is much less common, it may be confused for other entities, such as tuberculosis. Non-small cell lung cancer metastasizes to the bone in approximately 15–40% of cases, mostly involving the axial skeleton [11, 16]. Appendicular metastases are more common proximal to the knee and elbow, though more distal involvement is reported [5, 9, 11, 15, 18, 20, 21]. Extremity metastases are often initially misdiagnosed as benign entities such as infection due to presenting symptoms of local redness, pain, and swelling. Generally, a bony metastasis on radiograph appears as a lytic lesion and may be centered in the cortex (cookie-bite lesion). There may or may not be a demonstrable soft tissue mass [7]. Tuberculous and malignant involvement of the bone is often indistinguishable on imaging, particularly in the spine, where MRI findings can be similar [4, 13, 17, 23]. Diagnosis of tuberculous spread to the bone in general is often difficult, with an average delay in diagnosis of 16–19 months [4]. The musculoskeletal system is involved in 1–3% of cases of tuberculosis. The femur, tibia, and small bones of the hands and feet are often affected [6]. Typically, the metaphyses are involved, with radiographic features that include osteopenia and poorly defined lytic lesions with minimal surrounding sclerosis [4]. Our goal is to highlight the importance of maintaining a broad differential when evaluating a patient with confounding risk factors and imaging findings. Premature diagnoses may lead to delays in appropriate management [13]. Ultimately, tissue sampling may be necessary in providing a definitive, timely diagnosis.