Is my sons clonus more likley to be related to his cp or grade 4 ivh with pvl. ?

Cause/effect/symptom: My best answer is to segregate the terms you used into cause: (the hemorrhage) that produced: damage (injured neural pathways)that we call: "cerebral palsy" and the symptom: "clonus" that is caused by having injured neural pathways. So the hemorrhage does the damage, pvl is also damage related to injury & all this produces clonus. CP is just a term that lumps all the symptoms together in one name.

May be both: Clonus can be due to either or. Ivh w/pvl can cause cp.

Cerebral palsy: Ivh occurs in prematures, then resolves. Pvl is the result of changes in the brain due to prematurity. Cerebral palsy is a clinical diagnosis which includes spasticity and the ability to elicit clonus. This is often the result of events associated with prematurity. Clonus is a clinical finding that can be seen in normal children, but is more common in children with cerebral palsy.