A Stage 4 pressure ulcer (pressure injury) is characterized byfull-thickness tissue losswithextensive destruction, tissue necrosis, or damage to muscle, bone, or supporting structures. The key phrase in the question—“necrosis of soft tissue through the underlying muscle”—signals a depth of injury that extends beyond the subcutaneous tissue and involves muscle, which is consistent with Stage 4. By comparison, Stage 2 involves partial-thickness skin loss with exposed dermis (no necrosis through deeper structures). Stage 3 involves full-thickness skin loss where adipose may be visible, butmuscle, tendon, or bone are not exposed; undermining and tunneling may occur, yet the defining line is that it does not extend to muscle/bone involvement. “Stage 5” is not part of standard pressure ulcer staging used in coding and documentation. Outpatient CDI practice emphasizes documenting the exact stage, anatomic location, laterality when applicable, and whether the ulcer is healing or complicated (infection/osteomyelitis) because stage drives specificity, severity capture, and appropriate care planning documentation.