Low back pain indicative of psoas muscle metastasis and bronchopulmonary cancer

Muscle metastases of bronchopulmonary cancer are rare, notably when they are revealing. They can affect all muscles of the body with a predominance of psoas, diaphragmatic and para-vertebral muscles. We report a case of psoas muscle metastasis revealing bronchopulmonary cancer in a 40-year-old patient with a long history of smoking (30 packs of cigarettes/year) presenting a chronic left low back pain with asthenia and weight loss (15 kg/year). The clinical examination was unremarkable. An abdominal computed tomography scan showing a retroperitoneal mass at the expense of the left psoas muscle, lysing the L2 vertebral and left pedicle with intraspinal extension. A complement by cervico-thoracic computed tomography scan showed a lung mass with hilar and mediastinal lymphadenopathy. A scan-guided biopsy puncture of the psoas muscle mass identified its metastatic origin. The clinical picture is often deceptive leading to diagnostic and therapeutic delay, hence the interest of the imagery as well as histological confirmation is recommended.