Tremor Etiology in This Patient
The tremor in this 83-year-old frail woman is most likely medication-induced, with bupropion being the primary suspect, followed by metoprolol and levothyroxine as secondary considerations. Carcinoid syndrome itself does not cause tremor, and lanreotide (started after tremor onset) is unlikely to be the culprit.
Medication-Induced Tremor: Primary Culprits
Bupropion (100mg SR BID)
Bupropion is the most likely cause of this patient's tremor. The FDA label 1 documents that bupropion increases motor activity and produces CNS stimulant effects. In elderly patients with low body weight (<100 lbs), drug accumulation is particularly concerning because:
- Bupropion is extensively metabolized in the liver and excreted renally
- Elderly patients are more likely to have decreased renal function, increasing risk of adverse reactions
- The FDA specifically warns that "greater sensitivity of some older individuals cannot be ruled out" 1
Critical consideration: At her weight (<100 lbs) and age (83), this patient is receiving a relatively high dose that may be causing accumulation and tremor.
Metoprolol (75mg BID)
Beta-blockers paradoxically can cause tremor, particularly at higher doses. At 150mg total daily dose in a frail, underweight patient, this represents substantial beta-blockade that could contribute to tremor.
Levothyroxine (Synthroid 25mcg)
While the dose appears modest, even mild iatrogenic hyperthyroidism can cause tremor. Check TSH levels to exclude over-replacement, especially given her weight loss and frailty.
Carcinoid Syndrome Does NOT Cause Tremor
The classic carcinoid syndrome presentation includes flushing, diarrhea, episodic palpitations, lacrymation, and rhinorrhoea 2. Tremor is not a recognized feature of carcinoid syndrome. The guidelines from Gut 2 and NCCN 3 comprehensively describe carcinoid syndrome manifestations without mentioning tremor. Her diarrhea and weight loss are consistent with carcinoid syndrome, but the tremor requires a separate explanation.
Other Medications: Unlikely Contributors
- Amlodipine: Not associated with tremor; recent pharmacovigilance data 4 focus on metabolic effects, not neurological symptoms
- Atorvastatin: Myopathy possible, but tremor is not characteristic
- Naltrexone (4.5mg): Low-dose naltrexone at this dose is used for pain management 5 and is not associated with tremor
- Omeprazole: Neurological effects are rare 6; tremor not reported
- Fioricet (butalbital/acetaminophen/caffeine): The caffeine component could theoretically contribute to tremor, but at standard dosing this is less likely than bupropion
- Lanreotide: Started after tremor onset, so cannot be causal. Somatostatin analogues are not associated with tremor 3, 7, 8, 9
Recommended Diagnostic and Management Approach
Immediate Actions:
- Discontinue or reduce bupropion as a therapeutic trial. Given her frailty and low weight, this is the highest-yield intervention
- Check TSH to exclude thyrotoxicosis from levothyroxine over-replacement
- Review metoprolol necessity - consider dose reduction given her low body weight
- Assess renal function (creatinine, GFR) - critical for bupropion clearance 1
Clinical Monitoring:
- Observe for tremor resolution over 1-2 weeks after bupropion discontinuation (allowing for drug clearance)
- If tremor persists, consider metoprolol dose reduction
- Document tremor characteristics: resting vs. action, frequency, amplitude
Important Caveats:
Do not attribute the tremor to carcinoid syndrome - this would be a diagnostic error. The carcinoid tumors explain her diarrhea and weight loss (which improved with lanreotide), but not the tremor.
Frailty amplifies drug effects: At 83 years old, <100 lbs, with hepatic carcinoid metastases, this patient has reduced physiologic reserve. Standard doses become supratherapeutic. The bupropion 100mg SR BID may be excessive for her body habitus.
Polypharmacy consideration: With 20+ medications, drug-drug interactions are possible, though none of the specific combinations listed are known to cause tremor synergistically.