Hi there. Thank you for your question. I will be helping you out with your queries
With your symptoms, I think that you should have an MRI of your lower spine.
MRI will clarify whether it is a prolapsed disc causing sciatica or whether it is due to spread of tumor to your lower spine.
Meanwhile, if your pain is severe, you should be referred to a pain medicine specialist to assess you for a nerve block injection into your back to help you with your pain.
If that is not possible you will require strong anti-inflammatory medications along with nerve pain medications like gabapentin or pregabalin or duloxetine.
Let me know if you have more questions.
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many thanks for your clear reply - is it possile to have a reasoanble increased PSA level but actually have a greater chance of cancer spreading - hence the Sciatika pain ? is there cause for concern as I have actually not had any treatment so far ?