Feline thyroid storm (Proceedings)

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. VI. Other Unusual Manifestations of Feline Hyperthyroidism

Table 1

      A. Neurological

           i. Profound neuromuscular weakness

           ii. Dementia

           iii. Obtundation

           iv. Seizures

      B. Cardiovascular

           i. heart failure

           ii. pleural effusion

Table 2

           iii. pulmonary edema

           iv. pulmonary hypertension

           v. severe hypertensive disease