A patient describes an abnormal experience involving part of their body. Before revealing the answer, decide what distinguishes body image disturbance from a nihilistic delusion.

Ask what specifically has changed: the felt size, shape, position, or ownership of a body part, or a fixed belief that the part, or the person's existence itself, does not exist at all. Body image disturbance differs from a delusion about the body (such as a nihilistic delusion that a body part does not exist) in that body image disturbance is often, though not always, rooted in a demonstrable disturbance of sensory processing rather than a purely psychiatric belief system: the distortion concerns exactly what is perceived about the body, such as its size or ownership, without necessarily any fixed belief about non-existence. A nihilistic delusion, by contrast, is a fixed, false belief denying the existence of a body part, the self, or even the wider world, extending well beyond a distorted sensory experience into a delusional conviction. Whether the disturbance is a distorted sensory experience of the body versus a fixed delusional belief in non-existence is the key distinguishing feature.