In a 25-year-old male taking lithium and phenelzine (an irreversible MAOI), could phenelzine (or the combination of his medications) cause severe orthostatic hypotension and small‑fiber neuropathy that mimic seronegative autoimmune autonomic ganglionopathy?

{
  "question": "25-year-old male. Question: could his medicines, especially phenelzine, have caused or mimicked what Mayo diagnosed as seronegative autoimmune autonomic ganglionopathy/neuropathy (AAG)?\n\nTIMELINE\n- Lithium 5-7 years, never toxic; levels 0.7-1.4 recorded.\n- Phenelzine started at lower dose; raised to 75 mg/day. Pyridoxine prescribed for phenelzine, later stopped. Earlier B6 toxicity, resolved. Current PLP not measured.\n- Approximately 10-12 weeks after phenelzine start and BEFORE dose increase: subacute severe orthostatic hypotension (OH) with new ulcerative colitis. Then prednisone (40 lb gain), vedolizumab (now q4wk).\n- OH persists though bowel improved: supine 150/90, sitting 109/70, standing 90/70. Compensatory tachycardia, BP falls on exertion.\n- Worsening burning soles, fingertip allodynia, exhaustion, temperature intolerance, paradoxical psoriasis.\n\nTESTING\n- Mayo autonomic reflex screen: severe cardiovascular adrenergic failure; postganglionic sudomotor and cardiovagal function normal. Thermoregulatory sweat test normal.\n- Supine plasma NE low, 777 pmol/L (ref 1050-4800), on phenelzine. Standing NE not done.\n- Autoimmune dysautonomia panel negative.\n- Skin biopsy: thigh ENFD 5.9/mm (<1st percentile), distal leg borderline; non-length-dependent; Congo red negative.\n- Salt-wasting, low renin AND low aldosterone, 7 L/day urine.\n- Lifelong hyperhidrosis and polydipsia; joint hypermobility.\n- Mayo note does not list phenelzine or lithium.\n\nOTHER MEDS: tirzepatide since after onset (ongoing, well tolerated), atomoxetine and lisdexamfetamine 40 mg (used as pressors), IV ketamine q2wk, pregabalin/lorazepam PRN, lemborexant/temazepam, finasteride, botulinum toxin for migraine. Tried after onset: midodrine, pyridostigmine, fludrocortisone, nebivolol, ivabradine. Now proposed: droxidopa and IVIG 0.4 g/kg weekly x12.\n\nPsychiatric regimen decisions rest with his psychiatrist. I am asking about causation and how to interpret the diagnosis.\n\nQUESTIONS (cite sources, grade evidence)\n1. Can phenelzine cause OH this severe, and by what mechanism (false transmitter/octopamine, reduced NE release)? Typical onset timing and dose relationship? Does onset at a lower dose approximately 10-12 weeks after starting fit?\n2. Does selective adrenergic failure with normal sudomotor and cardiovagal function fit a drug effect better than AAG? How often is AAG this selective?\n3. Is supine NE interpretable on an irreversible MAOI? How does phenelzine change NE, DHPG and metanephrines? Which tests best separate drug effect from ganglionic failure?\n4. Is the autonomic reflex screen valid on phenelzine, atomoxetine and lisdexamfetamine? Should results be reinterpreted?\n5. Can phenelzine cause small fiber neuropathy directly or via pyridoxine deficiency, especially after B6 was stopped? Could earlier B6 excess explain the biopsy? Should PLP be checked now?\n6. Could long-term lithium, botulinum toxin, pregabalin or ketamine contribute to the OH, neuropathy, or low-renin/low-aldosterone salt-wasting? Could current tirzepatide be worsening the OH?\n7. Does a drug explanation weaken the AAG diagnosis? Could both be true (drug unmasking an immune process)?\n8. If phenelzine were the cause, what would a supervised dose reduction be expected to show, and how fast? Is that informative before committing to 12 weeks of IVIG?\n9. Rank: drug-induced vs immune vs combined, with reasoning."
}