LAUSR

Background Pulmonary hypertrophic osteoarthropathy (PHO) is a rare paraneoplastic syndrome that mainly occurs in patients with lung cancer. Most symptoms occur symmetrically, and unilateral symptoms without clubbing are infrequent. This report presents the case of a rare atypical symptom that was highly suspected of being PHO. Case presentation A 77-year-old woman with swelling and severe pain in the left femur for 2 months was referred to our hospital. Radiography revealed a remarkably osteogenic thickening and sclerotic lesion in her distal femur. Preliminary diagnoses of malignant bone tumor and hematological tumor were made based on laboratory test results, radiological examination, and clinical manifestation. A needle biopsy was performed, which ruled out the diagnosis of malignant bone tumors. A low-grade bone tumor was still suspected. After that, en bloc resection was performed, followed by replacement of the femur with a mega-prosthesis. Pathological analysis revealed no malignant tumor cells, and immunohistochemical staining for CDK4 and MDM2 yielded negative results. Meanwhile, pulmonary large cell carcinoma was identified on biopsy. Based on published studies, a diagnosis of atypical PHO was made according to clinical and imaging manifestations. Conclusions This is an infrequent case of PHO with unilateral symptoms in the left femur. When clinical manifestations and radiological findings are inconsistent with the pathological results, the possibility of benign lesions with malignant clinical manifestations or imaging features should be carefully considered.