Brief Answer:
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Detailed Answer:
I read your question carefully and I understand your concern.

Looking at your medical history it seems a difficult case in that you have several diagnosis which can both cause weakness and fatigue on their own as well as cause neuropathy.

Both lupus as well as hypothyroidism lead to an increased propensity for developing neuropathy. So the first step in the management is treating those two conditions. For hypothyroidism in particular it is important to follow up treatment with periodic TSH measurements in order to make sure the medication dosage is adequate, as hormone replacement dose may vary among patients, so it may be that you are under medication but not enough of it.

Also depending on how long you've been on steroids they can have side effects and lead to myopathy which also manifests with weakness. So if you have been using them for a long time that should be taken into account.

One other consideration to make is the need to complete tests. Your diagnosis is not complete without nerve conduction studies and electromyography (EMG) test. It is an essential part of neuropathy diagnosis and also will differentiate with other possible causes such as the steroid induced myopathy I mentioned.

Regarding treatment, if the MRI has evidenced back problems and those are considered as a possible cause, an important part is also physical therapy. If there is nerve root, cord or peripheral nerve compression also surgery may be considered.

To resume, neuropathy can be of different types and have many different causes, like thyroid dysfunction, lupus, compression of nerves in the spine. So the first step is to clear with your doctors which type you have and what is the main cause. Also if for a long time on steroids should exclude a myopathy.
Medication like Gabapentin do not alter the course of the disease, they only alleviate symptoms like pain. Only if cause is found and addressed (thyroid medication adjustments, surgery if needed, physical therapy) can the course of neuropathy be affected.

I remain at you disposal for other questions.

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Brief Answer:
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Detailed Answer:
Thank you for the update!

In view of the new information I do not think that Prednisone is the cause.

I still am not clear on the reason of your foot drop though. The nerve studies are not done to say you have foot drop, that should be noticed by the clinical exam, the nerve studies are done to elucidate the why. Foot drop may be due to lumbar spinal disease but also due to compression of a peripheral nerve or metabolic damage to peripheral nerves. So (also because it's been 7 years) I think nerve conduction studies are necessary. They are also necessary to evaluate the muscles as the muscle stiffness you mention shouldn't accompany foot drop, foot drop is related to flaccid paralysis normally.

I am not gonna lie and say that exams always are the solution, the causes of peripheral neuropathy are numerous and many blood and other tests are done to find the cause. Even after extensive testing in about 25% no cause is found, or in your case it might simply be left due to the connective tissue condition (lupus) which is known to affect many tissues. However before reaching to that conclusion some basic tests have to be completed and the conclusions on the cause be presented by your doctors.

If gabapentin caused you side effects it is ok to interrupt it, as I said it merely alleviates the symptoms not affect the course of the disease so should be used only if it provides benefit on how you feel. Another option for chronic neuropathic pain might be antidepressants like duloxetine, though as all drugs it has possible side effects.

I hope things work out for the best.

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