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A DTR (deep tendon reflex) Grade 4 signifies a hyperactive reflex response characterized by the presence of clonus. Clonus refers to a series of involuntary, rhythmic muscle contractions and relaxations that occur following a rapid stretch of the muscle. This finding indicates an upper motor neuron lesion or significant central nervous system dysfunction, which results in increased reflex activity.

In contrast, a normal response would typically be graded as Grade 2 and would indicate a balanced state of reflex activity. Slightly hyperactive responses may be indicative of a Grade 3, showing increased reflexes but without the rhythmic contractions of clonus. Total paralysis, which would correspond to a Grade 0, signifies an absence of any reflex activity or motor response, indicating a serious level of neuronal disruption. Thus, a Grade 4 response is distinctly marked by the notable hyperactivity and clonus, aligning with conditions that affect upper motor neuron pathways.