A 61-year-old woman was taking steroids for hypereosinophilic syndrome (HES). The patient experienced pain when the distal radius of the right forearm was punctured multiple times to secure the peripheral venous line. One month later, she developed swelling, numbness, and electric pain in her right forearm, which progressively worsened. She was referred to our department for differential diagnosis of complex regional pain syndrome (CRPS). Clinical findings other than pain and swelling were limited, and she did not meet the diagnostic criteria for CRPS. Ultrasonography revealed muscle hypertrophy and hyperechoic changes in the muscle and fascia. Similarly, MRI showed muscle hypertrophy and high signal intensity in the muscle and fascia, suggesting a muscle and fascial lesion. A biopsy of the muscle and fascia confirmed eosinophilic fasciitis caused by HES. Steroid pulse therapy was immediately administered, leading to rapid improvement in the tension and swelling of her right forearm.