Thyroid storm and unusual manifestations of feline hyperthyroidism (Proceedings)


Clinical signs, clinicopathologic abnormalities, diagnosis, and treatment.

1) Acute thyrotoxicosis

a) Precipitating event

b) Untreated thyrotoxicosis

c) Partially-treated thyrotoxicosis

d) Mortality in humans: 20-50%

2) Clinical signs

a) Accentuated clinical features of hyperthyroidism

b) Hyperpyrexia

c) Diaphoresis

d) Cardiac signs

i) Sinus tachycardia

ii) Cardiac dysrhythmia

iii) Tachyarrhythmias, atrial fibrillation

iv) Congestive heart failure

e) altered mental status; metabolic encephalopathy

i) agitation

ii) emotional instability

iii) seizures

iv) coma

f) vomiting

g) diarrhea

h) dehydration

i) hypovolemia

j) vascular collapse

k) abdominal pain

l) hypertension

m) retinal detachment; sudden blindness

3) Clinicopathologic abnormalities

a) Abnormalities associated with hyperthyroidism

i) Mild erythrocytosis

ii) Macrocytosis

iii) Mature neutrophilia

iv) Elevated liver enzymes

b) hyperglycemia

c) leukocytosis with left shift

d) elevated serum calcium

e) elevated total bilirubin

f) elevated creatine kinase

4) Diagnosis

a) Clinical signs

b) Abnormal thyroid hormone levels

c) Precipitating event

i) Thyroid surgery

ii) Infection, sepsis

iii) 131I therapy

5) Treatment

a) Thyrotoxicosis

i) Methimazole

(1) orally

(2) transdermally

(3) rectally

(4) prevent new hormone synthesis

ii) iodine preparations

(1) block release of preformed hormone

(2) iopanoic acid

(3) potassium iodide

(4) give 1 hour after first dose of methimazole

(5) may delay use of 131I

b) Block effects of hormone peripherally

i) B-blockers

(1) propanolol

(a) may block conversion of T4 to T3

(b) 2.5-5 mg bid-tid

(2) atenolol – 0.25-1 mg/kg po sid-bid

(3) esmolol - Loading dose of 200-500 mcg/kg IV over 1 minute; followed by a constant rate IV infusion of 25-200 mcg/kg/minute

ii) Anti-hypertensives

(1) amlodipine 0.625-1.25 mg/cat sid

(2) benazapril 0.25-1 mg/kg PO sid-bid

(3) hydralazine 2.5 mg PO bid

c) supportive care

i) cooling measures for fever

ii) fluids

iii) 5-10% dextrose

d) identification of precipitating cause

i) treat the cause

6) Other Unusual Manifestations of Feline Hyperthyroidism

a) Neurological

i) Profound neuromuscular weakness

ii) Dementia

iii) Obtundation

iv) Seizures

b) Cardiovascular

i) heart failure

ii) pleural effusion

iii) pulmonary edema

iv) pulmonary hypertension

v) severe hypertensive disease

Table 1

Diagnostic Criteria for Thyroid Storm in Cats

Thermoregulatory Dysfunction

Temperature > 104

Central Nervous System Effects




Extreme agitation


Altered mentation

Neuromuscular Effects

Neck ventroflexion

Lower motor neuron weakness

Gastrointestinal-Hepatic Dysfunction



Unexplained hyperbilirubinemia

Cardiovascular Dysfunction

Severe tachycardia

Cardiac arrhythmias

Congestive heart failure

Thromboembolic Disease

Precipitating cause

Impending thyroid storm should be considered if abnormalities as listed above in 3 or more separate organ systems are present. Based upon the Burch and Wartofsky algorithm for diagnosing human thyroid storm.5

Table 2: Medications Used In Thyroid Storm Patients

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