A 50-year old woman of Indian descent living in Denmark, with a prior history of knee arthrosis, presented with fever, myalgia and arthralgia which had developed during a return visit to New Delhi, India. Two weeks after returning to Denmark the generalised arthralgia and myalgia persisted to a degree where the patient was mainly confined to her bed. The symptoms were accompanied by extreme fatigue and fever sensation. When examined, the patient’s upper extremities were almost immobile due to soreness of shoulder, elbow and wrist joints, as well as reduced mobility of lower extremities, with slight edema of both feet. On inspection there were no visible signs of joint inflammation or skin rash. On admission we found elevated a sedimentation rate of 51 mm (normal range: 2–20 mm), C-reactive protein 25 mg/L (normal range: 0–10 mg/L), d-dimer 1, 9 FEU (fibrinogen equivalent units)/L (normal range < 0.5 FEU/L) and slightly elevated Lactate dehydrogenase at 212 U/L (normal range: 105–205 U/L). White blood cell count, creatinin kinase, antineutrophil cytoplasmic antibody, and antinuclear antibody were in the normal range. Dengue IgG and IgM were negative. NSAID treatment in combination with tramadole was initiated with no effect on the patient’s severe arthralgia. An 18F-FDG PET/CT (fluorine-18 fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography) was performed four weeks after debut of symptoms. Due to severe pain the patient was not able to place her right arm over her head during the scanning. The scan revealed pathological 18F-FDG uptake in enlarged lymph nodes on both side of the diaphragm, inflammation of both shoulder and hip joints, as well as 18F-FDG uptake in a nodule in the left breast. The main differential diagnoses were reactive arthritis, polymyalgia rheumatica, lymphoma or paraneoplastic phenomena. In response to these findings prednisolone 25 mg daily was initiated, which significantly relieved the patient’s symptoms within days. Concurrently, the patient was referred for further evaluation of the PET positive breast nodule, rheumatological evaluation, and a lymph node biopsy was considered.