Introduction: Malignant mesothelioma is a rare, aggressive neoplasia that affects the serous membranes. The pleural cavity is the most frequently affected area. Metastasis at the onset of the disease is rare, and muscular involvement is even more uncommon.
Case Report: We report a case of a 64-year-old non-smoking male, who had had intermittent exposure to asbestos for three years. He presented with dyspnea on moderate exertion that had developed over several days, discomfort in the left hemithorax, and some intolerance to decubitus positions. The patient had a weight loss of 10 kg in last three months. A chest X-ray showed bilateral pleural effusion with multiple nodular images in both hemithoraces. Computed tomography (CT) scans of the thorax and abdomen revealed multiple bilateral pleural and pulmonary lesions. We observed mediastinal lymphadenopathy, intra-abdominal implants, and a 56×40 mm polylobulated mass in the left buttock that underwent biopsy, revealing epithelioid cells that showed cytoplasmic positivity for keratins 5/6 and 7. We observed nuclear and cytoplasmic positivity for calretinin and nuclear positivity for the Wilms tumor 1 (WT1) protein, pointing to the diagnosis of metastatic malignant epithelioid mesothelioma. The medical and radiological history supported the diagnosis of primary pleural mesothelioma.
Conclusion: Initial presentation of pleural mesothelioma with distant metastasis outside the thorax is rare, and involvement of striated muscle even more unusual; only three such cases have been reported. The medical, radiological, and histological history of the patient prompted a differential diagnosis among metastases by carcinoma, mesothelioma, and sarcoma. The definitive diagnosis was established by histological and immunohistochemical study.