A 31-year-old man, with a family history of pulmonary tuberculosis, smoker 15 pack-years, presented to our consultation of pneumology with right latero-thoracic pain for three weeks associated with productive cough, night sweats and weightloss. Findings of physical examination were unremarkable. Electrocardiogram was normal. The hematology laboratory tests were also without abnormalities. The liver and renal functions were normal. The chest-X-Ray was also normal. Chest computed tomography (CT) revealed multiple bilateral excavated nodules with associated alveolar involvement made of ground glass nodules and parenchymal condensation of the right lower lobe. Bone window showed costal involvement of the middle arch of the 3rd left side with heterogeneous osteolytic lesion with invasion of the soft parts (Figure 1, Figure 2 ). The initial clinical presentation was in favor of pulmonary tuberculosis or pulmonary metastasis associated with bone metastasis. Pulmonary tuberculosis was suspected but overturned after the sputum mear results for Koch's bacillus was negative. Bronchial fibroscopy was refused by the patient. For anatomopathological confirmation, we accessed to the bone lesion since it is more accessible to biopsy. Needle biopsy of the rib lesion showed an abundant cellular infiltrate. This infiltrate contains sheets of oval mononuclear cells characterized by unique reniform or cleaved nuclei with pale cytoplasm and many eosinophils, plasma cells and lymphocytes are present with positive and diffuse staining with Cd1a (Figure 3 ).
Diagnosis of Langerhans cell histiocytosis (LCH) was retained.As part of the disease assessment, we completed by radiological explorations. MRI of brain and pituitary gland was normal. Bone scintigraphy showed a focus of hyper fixation in the sternum, the rest of the skeleton was of normal fixation.A level 2 analgesic has been prescribed .At 3, 6 and 12 months of follow-up, there was an improvement of pain with spontaneous resolution of the other symptoms.