Levothyroxine toxicity

Background

• Most acute thyroxine overdoses are mild.
• Chronic ingestions are more likely to present with clinical symptoms similar to thyrotoxicosis
• Diet pills such as Singaporean Slim 10 and athletic stimulant compounds can contain large amounts of T3/T4
• Thyrotoxicosis factitia - also known as thyroxine addict or metabolic malingerer where large doses of thyroid supplementation is taaking for weight loss or stimulation

Clinical Features

Although most thyroxine ingestions are mild, large acute or chronic ingestions can mirror moderate to severe thyrotoxicosis

Classic Triad

1. Hyperthermia
   • Often marked (40 - 41C)
2. Tachycardia
   • Often out of proportion to fever
3. Altered mental status (agitation, confusion, delirium stupor, coma, seizure)

May also have:

• Goiter
• Thyrotoxic stare, lid retraction
• Hyperhidrosis
• Thermoregulatory dysfunction
  • Fever
• Central nervous system dysfunction
  • Agitation, tremor
  • Delirium, psychosis, extreme lethargy
  • Seizure, coma
• Gastrointestinal-hepatic dysfunction
  • Diarrhea, nausea and vomiting, abdominal pain
  • Unexplained jaundice, hepatomegaly
• Cardiovascular dysfunction
  • Tachycardia, palpitations
  • Congestive heart failure, dyspnea
  • Pedal edema
  • A. fib
  • Widened pulse pressure

Differential Diagnosis

• Sympathomimetic ingestion
• Atherosclerosis
• Aortic regurgitation
• Thyrotoxicosis
• Fever
• Anemia
• Pregnancy
• Anxiety
• Patent ductus arteriosus
• Heart block
• Aortic dissection
• Endocarditis
• Increased ICP
• Vasodilating drugs
• Beriberi
• Pheochromocytoma

Management

• Management mirrors Thyroid storm treatment and depends on the degree of clinical symptoms