Will docs only diagnose cerebral palsy when there are definitive findings on mri? What clinical signs might they use instead?

Clinical diagnosis. CP is clasically defined as a motor disorder with no effect on cognition. The primary types are spastic diplegia (weakness and spasticity in both legs), spastic hemiplegia (one side of the body), triplegia (three extremities involved), and quadriplegia. An MRI is often helpful when making the diagnosis, but it is not always necessary. A good history and exam is usually sufficient.
Cerebral palsy. Doctors have diagnosed cerebral palsy for a great many years before the MRI was invented. There are numerous signs and symptoms of cerebral palsy and your physician can discuss this with you concerning the individual in question.
No. doctors will make the diagnosis of cerebral palsy based on clinical signs including spasticity, hyperactive reflexes, limitation of passive movement at joints. An abnormal MRI is not necessary for the diagnosis.