SN instructed patient and caregiver that the key difference between a suspected deep tissue injury (sDTI) and an unstageable pressure ulcer is that sDTI involves intact skin, whereas an unstageable ulcer involves a breakdown into at least the subcutaneous tissue. An unstageable ulcer is covered with necrotic tissue, such as slough or eschar, formed from remnants of the collagen matrix of subcutaneous tissue. So it’s always a full-thickness ulcer either stage III or stage IV.