Hypothyroidism: Presentation and Treatment
Hypothyroidism is characterized by fatigue, weight gain, cold intolerance, constipation, dry skin, and mental slowing, and is treated primarily with levothyroxine replacement therapy at 0.5-1.5 μg/kg/day, adjusted based on TSH levels monitored every 4-6 weeks until stable. 1, 2, 3
Clinical Presentation
Common Symptoms
- Fatigue and lethargy
- Weight gain
- Cold intolerance
- Constipation
- Dry skin (xeroderma)
- Mental impairment/poor concentration
- Depression
- Hoarseness
- Muscle aches (myalgias)
- Menstrual irregularities in women 2, 4, 5
Physical Examination Findings
- Bradycardia
- Edema
- Firm and irregular thyroid on palpation (in Hashimoto's thyroiditis)
- Delayed relaxation phase of deep tendon reflexes
- Periorbital puffiness
- Coarse, brittle hair 3, 4
Laboratory Abnormalities
- Elevated TSH (>4.0 mIU/L)
- Low free T4
- Elevated cholesterol levels
- Mild anemia
- Elevated creatine kinase 3, 6
Etiology
Primary Causes (99% of cases)
- Hashimoto's thyroiditis (chronic autoimmune thyroiditis) - most common in iodine-sufficient areas
- Iodine deficiency - most common worldwide
- Post-surgical hypothyroidism
- Post-radioiodine therapy
- Medications (amiodarone, lithium, immune checkpoint inhibitors)
- Subacute or chronic lymphocytic thyroiditis 1, 6, 5
Secondary/Tertiary Causes
Diagnosis
The diagnosis of hypothyroidism is primarily biochemical:
- Initial laboratory evaluation: Serum TSH with reflex testing of free T4
- Overt hypothyroidism: Elevated TSH with low free T4
- Subclinical hypothyroidism: Elevated TSH with normal free T4 3
Important: There is no role for imaging in the initial workup of hypothyroidism in adults. Imaging for thyroid morphology does not help differentiate among causes of hypothyroidism, and all causes will have decreased radioiodine uptake. 9
Treatment
Levothyroxine Therapy
- Starting dose: 0.5-1.5 μg/kg/day (lower doses for elderly or those with cardiovascular disease)
- Monitoring: Check TSH every 4-6 weeks until stable, then annually
- Dose adjustments: Make in 12.5-25 mcg increments until TSH normalizes
- Target: Normal TSH (0.4-4.0 mIU/L) 1, 7, 6
Special Considerations
Elderly Patients
- Start at lower doses (25-50 mcg/day)
- Increased risk of cardiovascular complications with overtreatment
- Monitor for atrial arrhythmias, especially atrial fibrillation 7
Pregnancy
- Increased levothyroxine requirements (approximately 30% higher)
- Monitor TSH monthly during pregnancy
- Maintain trimester-specific reference ranges
- Return to pre-pregnancy dose immediately after delivery 1, 7
Cardiovascular Disease
- Start at lower doses (12.5-25 mcg/day)
- Gradually increase to avoid cardiac stress
- Monitor for symptoms of angina or heart failure 1, 7
Complications of Untreated Hypothyroidism
- Cardiovascular disease (hyperlipidemia, atherosclerosis)
- Infertility and menstrual irregularities
- Myxedema coma (rare but life-threatening)
- Neurocognitive impairment
- In infants: mental retardation and delayed milestones 2, 5
Common Pitfalls in Management
- Inadequate monitoring: Failure to check TSH levels regularly
- Medication interactions: Taking levothyroxine with calcium, iron supplements, or certain foods
- Incorrect timing: Not taking levothyroxine on an empty stomach
- Inconsistent brand: Switching between different levothyroxine preparations with variable bioavailability
- Overlooking subclinical disease: Especially in high-risk populations 3, 4
Treatment Response
Most patients respond well to levothyroxine monotherapy, but approximately 10-30% of patients continue to experience symptoms despite normalization of TSH levels. In these cases, careful reassessment of the diagnosis and consideration of other contributing conditions is warranted before considering alternative treatments 6, 5.