Clinical Images: Acrometastasis: A rare mimicker of synovitis

The patient, a 74‐year‐old woman, was referred to an outpatient rheumatology clinic for assessment of osteoarthritis with pain over the base of her right thumb. Her hand x‐ray (A) showed advanced osteoarthritis of her right first carpometacarpal joint. She was treated with simple analgesics and a thumb splint. She returned six months later with (B) a two‐week history of pain, swelling, and pitting edema over the dorsum of her right hand and wrist. Screening blood samples for inflammatory arthropathy were negative, with minor elevation of markers of inflammation including an erythrocyte sedimentation rate of 39 mm/hr and a C‐reactive protein level of 28.6 mg/L. The pain and swelling persisted despite a short course of prednisone at 10 mg daily by her general practitioner. A repeat x‐ray (C) and magnetic resonance imaging scan of her hand demonstrated a large aggressive destructive lesion arising from the fourth metacarpal with bulky soft tissue component and involvement of the adjacent third and fifth metacarpals and carpal bones. She underwent further investigations and was diagnosed with primary adenocarcinoma of the lung with metastatic disease to the adrenals, multiple muscles, and bony metastases involving her right hand and rib. Bone metastases most commonly affect the axial skeleton, whereas involvement of the hands and feet, which are termed acrometastasis, is rare. Recognizing this is important because it may be the first indication of an occult malignancy and usually indicates disseminated disease. ¹ Lung cancer is the most common primary cancer with metastases to the digits. ¹ The hypothesized mechanism is hematogenous transport directly into the left atrium following venous erosion by the lung malignancy. ² Underrecognition of these lesions often contributes to misdiagnosis as synovitis, crystal arthropathy, or infection, leading to critical delays in treatment, and hence this is an important differential to consider. ¹

Supporting information

Disclosure form.