What is the best course of action for a 71 year old female with diabetes (hyperglycemia), hypertension, and essential tremor who presents with new onset jaw tremors while taking primidone (primidone) 100 mg every night (q hs) and metoprolol succinate (metoprolol succinate) 100 mg daily?

Evaluation and Management of New-Onset Jaw Tremor in a Patient on Primidone and Metoprolol

The most critical first step is to determine whether this jaw tremor represents progression of essential tremor, a medication-induced adverse effect (particularly from metoprolol), or an unrelated neurological condition requiring immediate evaluation.

Initial Diagnostic Approach

Distinguish Tremor Etiology

• Assess tremor characteristics: Determine if the jaw tremor is rhythmic, occurs at rest, with posture, or with action, and whether it differs from her baseline essential tremor pattern 1, 2

• Evaluate for drug-induced tremor: Metoprolol, while used to treat essential tremor in some patients, can paradoxically worsen or cause tremor in others, particularly at higher doses 3

• Rule out serious causes: Exclude Parkinson's disease (rest tremor, rigidity, bradykinesia), hyperthyroidism, metabolic derangements from poorly controlled diabetes, or structural brain lesions 4

• Check medication adherence and timing: Verify she is taking primidone consistently, as jaw tremor can emerge if essential tremor is inadequately controlled 5

Immediate Management Considerations

Optimize Current Tremor Therapy

If the jaw tremor represents progression of essential tremor despite current therapy, increase primidone dosage before adding additional agents 1, 2:

• Current dose of primidone 100 mg nightly is subtherapeutic; therapeutic range is 50-250 mg/day divided or as a single dose 5
• Increase primidone gradually (by 50 mg increments every 1-2 weeks) to minimize acute adverse reactions, which occur in 32% of patients 5
• Target dose: 150-250 mg daily, monitoring for sedation, ataxia, and nausea 1, 2

Address Potential Beta-Blocker Issues

Consider that metoprolol may be contributing to the problem rather than helping 3:

• Metoprolol succinate 100 mg daily is within therapeutic range but may cause tremor as an adverse effect in some patients 3
• If metoprolol is being used primarily for hypertension (not essential tremor), consider switching to a non-beta-blocker antihypertensive such as an ACE inhibitor or calcium channel blocker 3
• If metoprolol is being used for tremor control, propranolol (30-160 mg/day) is more effective for essential tremor than metoprolol 1, 2, 4

Combination Therapy Strategy

If primidone optimization alone is insufficient, add propranolol rather than continuing metoprolol 1, 2, 5:

• Propranolol combined with primidone provides superior tremor control compared to either agent alone 1, 5
• Start propranolol at 30-60 mg/day in divided doses or as long-acting formulation, titrating to 40-160 mg/day 1, 4
• Monitor for hypotension, bradycardia, and bronchospasm, particularly given her age and diabetes 3

Special Considerations in This Patient

Age-Related Factors

• At 71 years old, she is at higher risk for medication adverse effects including hypotension and falls 3
• Beta-blockers can mask hypoglycemia symptoms in diabetic patients, requiring careful glucose monitoring 3
• Start with lower doses and titrate slowly to minimize adverse effects 3

Diabetes Management

• Ensure her diabetes is well-controlled, as hyperglycemia can worsen tremor 3
• Beta-blockers may affect glucose metabolism and mask hypoglycemia warning signs 3
• Monitor blood glucose more frequently if adjusting beta-blocker therapy 3

Alternative Agents if First-Line Therapy Fails

If primidone and propranolol combination is ineffective or not tolerated 1, 2:

• Topiramate: 25-400 mg/day, effective for limb and head tremor 1, 2
• Gabapentin: 300-3600 mg/day in divided doses 1, 2
• Clonazepam: 0.5-6 mg/day, particularly if anxiety exacerbates tremor 1, 4

Critical Pitfalls to Avoid

• Do not use sliding-scale insulin or rely solely on reactive glucose management in this diabetic patient; ensure she has a structured regimen 3
• Do not continue metoprolol if it is ineffective for tremor; propranolol is the beta-blocker of choice for essential tremor 1, 2, 4
• Do not delay evaluation if tremor is asymmetric, associated with rigidity, or accompanied by other neurological signs suggesting Parkinson's disease 4
• Monitor for acute primidone toxicity (ataxia, sedation, nausea) when increasing doses, as 32% of patients experience acute adverse reactions 5

Surgical Referral Threshold

Consider neurosurgery referral for deep brain stimulation if 1, 2:

• Tremor remains disabling despite optimal medical therapy with primidone and propranolol
• Quality of life is significantly impaired by tremor
• Patient is willing to undergo surgical intervention (90% tremor control rate with deep brain stimulation) 1