What are the next steps for a 45-year-old male with ulcerative colitis, depression, schizophrenia spectrum, asthma, and cannabis misuse disorder, presenting with suppressed Thyroid Stimulating Hormone (TSH) and elevated free T4, and tachycardia?

Immediate Management of Thyrotoxicosis with Tachycardia

This patient has overt thyrotoxicosis (suppressed TSH <0.01 with elevated free T4 of 20) and symptomatic tachycardia at 116 bpm, requiring immediate beta-blocker therapy and urgent endocrinology referral to determine the underlying cause and prevent cardiovascular complications.

Immediate Actions (Within 24-48 Hours)

1. Initiate Beta-Blocker Therapy

• Start propranolol 20-40 mg orally 3-4 times daily OR atenolol 25-50 mg once daily immediately to control tachycardia and prevent thyroid storm 1
• Titrate dose to achieve heart rate <90 bpm if blood pressure tolerates 1
• This is critical given his existing tachycardia of 116 bpm and multiple comorbidities

2. Urgent Additional Laboratory Testing

Order the following tests immediately (preferably at 8-9 AM):

• Morning cortisol (8 AM) and ACTH to rule out central hypophysitis, which can present with low TSH and elevated T4 1
• Total T3 or free T3 to assess severity of thyrotoxicosis 1
• TSH receptor antibodies (TRAb or TSI) and thyroid peroxidase (TPO) antibodies to differentiate Graves' disease from thyroiditis 1
• If premenopausal female or male: LH, FSH, testosterone/estradiol to screen for panhypopituitarism 1

Critical consideration: The combination of suppressed TSH with elevated free T4 could represent either primary thyrotoxicosis OR central hypophysitis (where TSH can be inappropriately "normal" or low-normal despite elevated T4) 1. You must check morning cortisol urgently because if this is hypophysitis with adrenal insufficiency, the patient is at risk for adrenal crisis 1.

3. Thyroid Imaging

• Order thyroid ultrasound to assess for nodules, diffuse enlargement, or thyroiditis 1
• Consider radioactive iodine uptake scan (RAIUS) or Technetium-99m scan if available and patient hasn't had recent iodinated contrast, to differentiate Graves' disease (high uptake) from thyroiditis (low uptake) 1

Differential Diagnosis Priority

Most Likely: Primary Thyrotoxicosis

Thyroiditis (most common with this presentation):

• Self-limiting inflammatory process causing transient thyrotoxicosis followed by hypothyroidism 1
• Low/absent radioiodine uptake on scan 1
• Typically painless but can have painful variant 1
• Expected to transition to hypothyroidism within 1-2 months 1

Graves' Disease (less likely but must exclude):

• Positive TSH receptor antibodies 1
• High radioiodine uptake 1
• May have diffuse goiter 1

Must Exclude: Central Hypophysitis

This is critical because:

• Can present with low TSH and elevated free T4, mimicking primary hyperthyroidism 1
• If morning cortisol is low (<5-10 mcg/dL depending on assay), this patient needs immediate hydrocortisone replacement BEFORE any thyroid treatment to prevent adrenal crisis 1
• Requires MRI of sella turcica with pituitary cuts 1
• While rare with his medication list (no immune checkpoint inhibitors), it remains in differential for any patient with this biochemical pattern 1

Rare but Consider: TSH-Secreting Pituitary Adenoma

• Elevated or inappropriately normal TSH with elevated free T4 2, 3
• Would require pituitary MRI and alpha-subunit measurement 2
• Very rare cause 2

Monitoring and Follow-Up

Short-Term (Next 2-3 Weeks)

• Repeat TSH, free T4, and free T3 every 2-3 weeks to monitor for transition from thyrotoxic phase to hypothyroid phase if thyroiditis is confirmed 1
• Monitor heart rate and symptoms daily
• If morning cortisol comes back low, start hydrocortisone 20 mg AM/10 mg noon immediately and delay any thyroid hormone treatment for at least 1 week 1

Urgent Endocrinology Referral

• Refer to endocrinology within 1 week for definitive diagnosis and management plan 1
• Endocrinology consultation is particularly important given the complex medication list and multiple comorbidities

Critical Medication Considerations

Review Current Medications

Abilify (aripiprazole) 20 mg: While atypical antipsychotics are not commonly associated with thyroid dysfunction, document this for endocrinology review

Do NOT start antithyroid medications (carbimazole, methimazole) empirically without confirming diagnosis, as thyroiditis is self-limiting and does not require antithyroid drugs 1

Red Flags Requiring Emergency Department Evaluation

Send to ED immediately if patient develops:

• Heart rate >120 bpm at rest despite beta-blocker
• Fever >38.5°C (suggests thyroid storm)
• Altered mental status, confusion, or agitation
• Severe tremor, agitation, or psychosis
• Chest pain or dyspnea
• Symptoms of adrenal crisis: severe weakness, hypotension, nausea/vomiting, abdominal pain 1

Expected Clinical Course

If Thyroiditis (Most Likely):

• Thyrotoxic phase lasts 1-4 weeks 1
• Transition to hypothyroidism occurs within 1-2 months of symptom onset 1
• Will likely need levothyroxine replacement long-term 1
• Continue beta-blocker during thyrotoxic phase, then taper as free T4 normalizes 1

If Graves' Disease:

• Requires antithyroid medication (methimazole preferred) or radioactive iodine ablation 1
• Beta-blocker continued until euthyroid 1

Documentation for Colleague

Leave clear note stating:

• Beta-blocker started with specific dose and target heart rate
• Labs ordered with specific rationale (especially morning cortisol to rule out hypophysitis)
• Endocrinology referral placed as urgent
• Patient instructed on red flag symptoms requiring ED evaluation
• Plan for repeat thyroid function tests in 2-3 weeks
• Explicit instruction: If morning cortisol returns low, start hydrocortisone immediately and contact endocrinology emergently 1