Could a disc herniation (l4, l5)lead to permanent nerve damage. if so what are signs of nerve damage around l4, l5 does nerve damage show on a mri?

It is possible: If any nerve is compressed severely for a long time it can be permanently damaged damage at l4- could cause foot drop it is possible to see compression on MRI but injury would not necessarily be seen.

Yes: The usual nerves involved at that level is the l 5 nerve root. It controls elevation of the foot muscles and sensation to the outside of the foot including the big toe. Compression of the nerve by a herniated disc can be identified on an mri. The functioning of the nerve can not.

Yes if nothing done: If a heniated disc is pinching the nerve producing a weak leg/foot drop/decreased patellar or ankle reflex, numbness then the longer this continues the less likely the nerve will be normal when fixed.Like paking a car on the garden hose. 1 or 2 days it comes back to normal but after 1 month its flat forever.Mri shows the herniation or pinch.Emg or above symptoms shows nerve damage.

compression shows : Prolonged pressure on the nerve can cause nerve damange, sometimes permanent. Nerve damage signs include weakness and sensory changes (numbness/tingling) in the area of the nerve. For l4, 5 that is typically weakness and tingling/numbness in the lower leg/foot area. An MRI will show the discs and potential pressure/impingement on the nerve root(s).

Yes: Numbness in foot near big toe and weakness raising foot or toes. Nerve damage does not show on an MRI but you can tell that there is pressure on the nerve from the disc.