Well, it could be and maybe not. Central pain syndrome, does exist, and people with MS may get it due to brain lesions.

It would not remit and recur and have good days and bad like the PN does, however, to the same extent.

The risks with nortriptyline involve hyper-thyroidism not hypo. The warning includes levothyroxine because when people are given medications sometimes there are high dose titration errors, which are temporary hyper-events. Elevated thyroid levels lead to cardiac events by themselves, so the warning with the TCA potential exists for that reason..additive stress on the heart. Also stimulants can interact with nortriptyline, and in the ADHD population there have been a handful of children taking both Ritalin and nortriptyline that have had fatal cardiac events. TCAs can also cause photosensitivity reactions with sun exposure. I personally think in the extreme reactions with the heart, that low magnesium and low potassium can be the triggers.
The long QT research shows that now.
Here is a link with drug lists for it:
http://www.azcert.org/medical-pros/d...drug-lists.cfm

TCAs have a potential to affect heart rhythm and therefore that is why they are not commonly used for depression anymore. Typical doses for depression are much higher, and with nortriptyline would be 50mg a day and above. The very low doses used for pain, are less risky. People with a genetic tendency to long QT syndrome should avoid TCAs completely. This however, can be screened for with an EKG. Having an EKG before treatment as a base line, and then during treatment with the TCA will show any abnormalities should they appear.

As far as the skin biopsy goes: Tests only show one snapshot in time for a person. The biopsy does not give a conclusive result in individual cases, unless repeated, showing changes over time. It is relatively new, and interpretation in people is still just that, an interpretation. It could be you always had fewer nerve endings, genetically. It could be those nerves decline with aging normally. You don't know what you had when you were 30 or 50, for example.
(sensory nerves and perception tend to decline with age for everyone to some extent).

TCAs do work for some people, so don't write them off just yet.
If you feel you are improving some, without them, you can delay that decision. But before taking them, it is always best to have the EKGs, esp at your age. Treatment of central pain syndromes varies with the person. If really severe discomfort is present then doctors go for anti-seizure drugs too. But these cause serious problems in the elderly--hyponatremia-- for one.
Alot depends on you and how you handle this discomfort, and how severe it is, and whether it progresses or not. Things like that should be considered too.