Background and Clinical Significance Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine skin malignancy. Early diagnosis is essential to optimize therapeutic strategies and improve prognosis. However, the role of high-frequency ultrasound (HFUS) in the diagnostic and follow-up phases of MCC remains under-investigated and underutilized in clinical practice. Case Presentation We present a case of MCC initially referred to a physiatric outpatient clinic for a functional disorder of the third finger, where HFUS revealed a well-circumscribed, hypoechoic subdermal lesion with central and peripheral vascularity. Surgical excision, histopathology, and immunohistochemistry confirmed the diagnosis of Merkel cell carcinoma. The HFUS findings were correlated with histological features, and a structured sonographic follow-up protocol was established postoperatively. Conclusions This case highlights the diagnostic and prognostic potential of HFUS in MCC, especially in early detection, surgical planning, and longitudinal follow-up. A multidisciplinary approach integrating ultrasound imaging, surgery, and pathology may enhance diagnostic accuracy and patient management.