S3753 An Atypical Clue to Colorectal Carcinoma: When Hip Pain Unmasks Stage IV Disease

Introduction: Colorectal cancer (CRC) is the third most common malignancy worldwide, typically presenting with gastrointestinal symptoms such as hematochezia, altered bowel habits, or iron-deficiency anemia. Initial presentation with isolated musculoskeletal or neuropathic pain—particularly without bone metastasis—is exceedingly rare. Such atypical symptoms can delay diagnosis and treatment. We report a case of metastatic CRC initially presenting as isolated hip and thigh pain due to suspected retroperitoneal spread involving the femoral nerve. Case Description/Methods: A 59-year-old man with a history of coronary artery disease, insulin-dependent type 2 diabetes, hypertension, hyperlipidemia, and former tobacco use presented with acute right hip pain radiating to the anterior thigh. He denied trauma, bowel habit changes, weight loss, or systemic symptoms. Physical exam showed intact strength and sensation without atrophy. Laboratory tests revealed leukocytosis, elevated alkaline phosphatase, and mild transaminitis. X-rays of the hip and femur were unremarkable. Abdominal ultrasound revealed multiple hepatic lesions. MRI and computed tomography abdomen/pelvis showed numerous liver metastases, pulmonary nodules, and focal cecal wall thickening. Colonoscopy identified a friable cecal mass; biopsy confirmed poorly differentiated adenocarcinoma. Liver biopsy confirmed metastatic colonic origin. Bone scan was negative for osseous involvement. Given the pain distribution and lack of musculoskeletal lesions, lateral femoral cutaneous nerve involvement from retroperitoneal tumor spread was suspected. Discussion: CRC commonly metastasizes to the liver, lungs, and lymph nodes. Skeletal muscle metastases are rare (<0.03%), and neuropathic pain due to retroperitoneal involvement is even less frequently described as an initial presentation. Femoral neuropathy may manifest as anterior hip and thigh pain, sometimes mimicking musculoskeletal conditions. In this case, metastatic retroperitoneal spread likely compressed or infiltrated the femoral nerve, resulting in neuropathic symptoms in the absence of direct osseous or muscular metastasis. While femoral neuropathy has been reported in CRC recurrence, its role as an initial clue to diagnosis is poorly documented. This case highlights the importance of considering malignancy in patients with unexplained localized pain and supports early use of advanced imaging and endoscopic evaluation to avoid delays in diagnosis.