First off ill assume that they have ruled out the common causes including diabetes, which would be the first thing i would consider. A simple HbA1c test or FASTINg glucose levels should be able to rule this out. While staying on the endocrine system, i would like to rule out simple causes first which would include the thyroid as wel. Thyroid disorders are common and both hypothyroidism and hyperthyroidism in the beginning can cause symptoms like these. I hope your PCP has ruled out thyroid disorders as well. Also addisons disease which can cause the tremors etc is another possibility in which there is decreased production of cortisol in the body and that too should be considered here. Urinary cortisol levels are way to diagnose this problem.
As you can see im not restricting myself to simply neurological disorders, there are various causes of these issues even though some of the symptoms of these disorder dmay not fit in your case, they should be considered as each of the above disorders can present in a variety of ways. Continuing on this theme, autoimmune issues are something which can be considered especially vasculitis given the lesions that you have been experiencing. A simple ESR and ANA level should be done and if the suspicion is high enough then specialized tests like ANCA or a complete ENA profile should be considered as well.
now regarding porphyria that is a possibility to be considered but there are various types of porphyria and the commonest type is AIP or acute intermittent prophyria, if this was opresent here then you should have had some other symptoms like dark colored urine and abdominal or even neuropathy like symptoms. Other types of porphyria would have more extensive rashes. While it is possible, it is less likely given the information that you have provided. Regarding systemic mastocytosis, if that was the case then mast cells should have been increased your system and that should have shown up as increased eosinophils, basophils, monocytes or even platelets in the CBC which i assume was not the case. The only significant abmormality is a high ketone level which can be due to fasting before the tests or due to decreased intake over the last few days.
I think rather than more complicated diagnosis like systemic macrocytosis or porphyria, we should concentrate on RULING OUT simple things like endocrine and autoimmune issues first, those should be the first priority and if that is ruled out then we should look into the other causes. But i feel we should not restrict ourselves to simply the nervous system, these symptoms are too broad and can be due to other issues such as the ones i have highlighted above.
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