Miliary tuberculosis in a patient with metastatic thymoma

Clinical History

A 64 year-old female comes to the ER with persistent fever for the last two weeks.
She is being followed by oncology for a stage IV thymoma with multiple pleural metastasis and receives treatment with taxol, carboplatin and steroids.

Chest X-Ray findings and CT scan were performed.

Imaging Findings

The chest X-ray showed a miliary pattern consisting of profuse tiny, discrete, rounded
pulmonary opacities of uniform size (3mm) and diffuse distribution throughout the lungs [5]. There is also evidence of pleural metastasis in the right chest. There is medistinum enlargement and lateralization to the right chest suggesting atelectasis.

The admission CT scan confirmed the presence of randomly distributed micronodules, also known as miliary pattern [5] (Figure 2).

The previous CT scans showed multiple thymoma metastasis following its characteristic pleural dissemination (Figure 3).

With the antecedent of a oncological disease we have to perform a differential diagnosis with: hematogenous metastatic pulmonary disease and lymphangitic carcinomatosis. As a immunocompromised patient we must consider miliary infections such as tuberculosis.

Microbiology findings of the bronchoalveolar lavage confirmed tuberculosis.

Discussion

Miliary tuberculosis is an uncommon (1% of all patients with any form of tuberculosis) presentation of TBC that occurs when a primary tuberculosis focus infiltrates a pulmonary vein spreading the infection through all tissues. Lungs, liver and spleen are the most common targets of miliary TB metastasis [1].

Miliary tuberculosis has a mild clinical and a poor prognosis. The most frequent clinic presentations are: fever, fatigue, anorexia, weight loss and hepatomegaly[1]. When a immune compromised patient presents this symptomatology we must include this entity in the differential diagnosis. Since this is a life threatening disease we should start empiric treatment.

The first radiological approach can be done with chest X-Ray. The classical presentation of this diseases is a reticulonodular infiltrate with a homogeneous distribution that affects instinctively both the interstitium and the alveolar space. This finding in an immunocompromised patient with subacute symptomatology is highly suggestive of miliary tuberculosis. To determine the exact pattern and establish a differential diagnosis a CT scan must be performed [2].

Classical findings of pulmonary tuberculosis such as tree-in bud condensations and centrilobular nodules in patients with compatible clinic presentation have proven to have a positive correlation with active TB diagnosis even when other means of diagnosis (sputum culture, BAL) fail to reach the diagnosis. [3]

As we can see in the images, our patient had thymoma metastatic disease confirmed by a biopsy in 2011 that was staged as IV B2. As we can see on Figure 3 thymoma usually follows a unilateral metastatic pattern and can also affect pericardial cavity (as shown in CT scan images) [4]. The dimensions of metastatic implants compromised patient's cardiac function, a metastasectomy was performed in 2016.

The miliary pattern allows us to discard the possibility of lymphangitic carcinomatosis since this disease has a perilymphatic micronodular pattern (Figure 4). This pattern is characterized by distribution along or adjacent to the lymphatic vessels in the lung: this is perihilar, peribronchovascular, and centrilobular interstitium, as well as in the interlobular septa and sub-
pleural locations. Alveoli do not have lymphatics [5].

As we have seen in this case thymoma metastatic disease usually affects pleural cavities, haematological dissemination is rare. We had no evidence of other primary hematological disseminating tumor.

Since the most probable diagnosis was miliary tuberculosis a bronchoalveolar lavage was performed, the PCR results were positive for M. tuberculosis sensible to isoniazid and rifampicin.

Written informed patient consent for publication has been obtained.

Differential Diagnosis List

Final Diagnosis

Miliary tuberculosis

URL:	https://eurorad.org/case/16191
DOI:	10.1594/EURORAD/CASE.16191
ISSN:	1563-4086