Non-small cell lung cancer presenting as "psoas muscle syndrome".

Lung cancer is the leading cause of cancer-related death worldwide and majority of patients are diagnosed in advanced/metastatic disease stage. Sites of distant metastases mainly include contralateral lung, lymph nodes, brain, bones, adrenal glands and liver; skeletal muscles metastases (SMMs) are less common. Psoas muscle and diaphragm metastases are mainly found during autopsy, as their involvement commonly is asymptomatic. We report a case of a 60-year-old female, suffering from non-small cell lung cancer (NSCLC), with refractory lower back pain, as expression of malignant psoas syndrome (MPS). MPS is a rare and difficult-to-treat cancer-pain syndrome, unresponsive to majority of analgesic therapy, related to psoas muscle metastasis; it is usually caused by different tumors such as uterus, ovary, bladder, prostate, colon-rectum, lymphoma, melanoma and sarcoma and represents an uncommon finding in NSCLC patients.