An endocrine cause of stupor after myocardial infarction

T X S Freeth, MB ChB

Registrar, Department of Medicine, Groote Schuur Hospital and University of Cape Town

I L Ross, MB ChB, FCP (SA), Cert Endocrinology & Metabolism, PhD Medicine

Senior Consultant Endocrinologist/Senior Specialist Physician, University of Cape Town and Groote Schuur Hospital, Cape Town

A 68-year-old woman presented with stupor (Glasgow coma score 11/15), severe sinus bradycardia (36 beats/minute) and bradypnoea (6 breaths/minute), after being bed-bound for a prolonged period owing to extreme lethargy. She was taking 200 mg amiodarone twice daily. The amiodarone had been initiated 9 months previously for arrhythmia control post-myocardial infarction.

General examination revealed coarsened facies, hoarseness and central obesity. Thyroid-stimulating hormone was un-recordably high. Free T3 was 0.7 pmol/l. Free T4 was 3.7 pmol/l. Baseline thyroid function had not been tested. A diagnosis of severe amiodarone-induced hypothyroidism was inferred.

Renal function initially deteriorated rapidly and pyelonephritis became unmasked, resolving on antibiotics. With amiodarone discontinuation and cautious thyroid replacement, the patient regained functional independence for the first time in four months.

Discussion

Because of its iodide-containing moiety, amiodarone can induce either thyrotoxicosis (Jod-Basedow mechanism) or hypothyroidism (Wolff-Chaikoff mechanism).1 Local data suggest a trend to the inevitability of developing thyroid disease the longer a patient is on amiodarone.2

This case illustrates several important clinical points:

• Maintenance dosing of amiodarone is usually 200 mg once daily or less.3

• Amiodarone’s half-life is extremely long (up to 4 months);3 toxicity cannot rapidly be reversed.

• It is imperative to know the free T3 level in amiodarone-induced thyroid disease.

• Thyroxine and tri-iodothyronine replacement in severe hypothyroidism must be cautious; overzealous therapy precipitates pulmonary oedema, myocardial infarction and arrhythmias.4

• Sepsis in myxoedema is often occult and causes mortality.5

• Thyroid function testing before and during amiodarone therapy is mandatory.

Amiodarone therapy guidelines for South Africa are currently being developed and should be available in the near future.

References

1. Loh KC. Amiodarone-induced thyroid disorders: a clinical review. Postgrad Med J 2000; 6:133-140. (Accessible online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1741517/pdf/v076p00133.pdf)

1. Loh KC. Amiodarone-induced thyroid disorders: a clinical review. Postgrad Med J 2000; 6:133-140. (Accessible online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1741517/pdf/v076p00133.pdf)

2. Ross IL, Marshall D, Okreglicki A, Isaacs S, Levitt NS. Amiodarone-induced thyroid dysfunction. SAMJ 2005;95:180-183. (Accessible online at http://www.samj.org.za/index.php/samj/article/viewFile/1585/949)

2. Ross IL, Marshall D, Okreglicki A, Isaacs S, Levitt NS. Amiodarone-induced thyroid dysfunction. SAMJ 2005;95:180-183. (Accessible online at http://www.samj.org.za/index.php/samj/article/viewFile/1585/949)

3. Rossiter D, ed. South African Medicines Formulary. 10th ed. Cape Town: Health and Medical Publishing Group, 2012:132-133.

3. Rossiter D, ed. South African Medicines Formulary. 10th ed. Cape Town: Health and Medical Publishing Group, 2012:132-133.

4. Gardner DG, Shoback D. Greenspan’s Basic and Clinical Endocrinology. San Fransisco: McGraw-Hill, 2011:197-198.

4. Gardner DG, Shoback D. Greenspan’s Basic and Clinical Endocrinology. San Fransisco: McGraw-Hill, 2011:197-198.

5. Yamamoto T, Fukuyama J, Fujiyoshi A. Factors associated with mortality of myxedema coma: report of eight cases and literature survey. Thyroid 1999;9:1167-1174. (Accessible online at http://www.ncbi.nlm.nih.gov/pubmed/10646654

5. Yamamoto T, Fukuyama J, Fujiyoshi A. Factors associated with mortality of myxedema coma: report of eight cases and literature survey. Thyroid 1999;9:1167-1174. (Accessible online at http://www.ncbi.nlm.nih.gov/pubmed/10646654