In a patient receiving phenelzine (an irreversible MAOI) along with lithium, tirzepatide, and other agents, who developed severe orthostatic hypotension, low supine plasma norepinephrine, selective adrenergic failure, and small‑fiber neuropathy, could phenelzine be the cause and mimic seronegative autoimmune autonomic ganglionopathy, and what tests or clinical features can distinguish a drug‑induced effect from true autoimmune autonomic ganglionopathy?

{
  "question": "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 yrs, never toxic; levels 0.7-1.4 recorded.\n- Tirzepatide from mid-[DATE], stopped [DATE] when GI symptoms began.\n- Phenelzine started late [DATE] at lower dose; raised to 75 mg/d [DATE]. Pyridoxine prescribed for phenelzine, later stopped. Earlier B6 toxicity, resolved. Current PLP not measured.\n- [DATE], ~10-12 wks 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/d urine.\n- Lifelong hyperhidrosis and polydipsia; joint hypermobility.\n- Mayo note does not list phenelzine or lithium.\n\nOTHER MEDS: 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 ~10-12 wks 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, tirzepatide (rapid weight loss, abrupt stop), botulinum toxin, pregabalin or ketamine contribute to the OH, neuropathy, or low-renin/low-aldosterone salt-wasting?\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."
}