When you state PNS, does this stand for peripheral nerve stimulation or peripheral subcutaneous field stimulation. If so this would not fall under 63685 since 63685 is for a dorsal column stimulator/neurostimulator.
Below is codes used for PNS or PSFS
64590 Insertion or replacement of peripheral or gastric neurostimulator pulse generator or receiver, direct or inductive coupling
0284T Revision or removal of pulse generator or electrodes, including imaging guidance, when performed, including addition of new electrodes, when performed
If this is for a neurostimulator, the NCCI policy manual states the following describing a pulse generator removed on the right and a new generator placed on the left, they state it would be appropriate to use 63685 63688-59. In regards the lead extension, it is a gray area if this falls under 63685 for the tunneling or could be represented to a revision to the existing lead with 63663 for a neurostimulator leads:
16. The following information was revised and published April 1, 2012. CPT codes 61885, 61886, and 63685 describe ?insertion or replacement? of cranial or spinal neurostimulator pulse generators or receivers. Reporting an ?insertion or replacement? CPT code necessitates use of a new neurostimulator pulse generator or receiver. CPT codes 61888 and 63688 describe ?revision or removal? of cranial or spinal neurostimulator pulse generators or receivers. If the same pulse generator is removed and replaced into the same or another skin pocket, the ?revision? CPT code is the only CPT code that may be reported. The ?replacement? CPT code which requires use of a new neurostimulator pulse generator or receiver should NOT be reported as this Manual previously indicated. If one pulse generator is removed and replaced with a different pulse generator into the same or another skin pocket, the ?replacement? CPT code may be reported. The ?removal? CPT code is not separately reportable. The ?insertion or replacement? CPT code is separately reportable with a ?revision or removal? CPT code only if two separate batteries/generators are changed. For example, if one battery/generator is replaced (e.g., right side) and another is removed (e.g., left side), CPT codes for the ?insertion or replacement? and ?revision or removal? could be reported together with modifier 59.