The case today focused on a patient with a recent diagnosis of pulmonary blastomycosis on itraconazole who was admitted with weakness: the patient was found to be hyporeflexic and hypokalemic with a prolonged QTc and undetectable TSH. The patient was ultimately diagnosed with Thyrotoxic Periodic Paralysis.
Thyrotoxic Periodic Paralysis = Transient, recurrent episodes of flaccid muscle paralysis of Proximal > Distal muscles
- ALMOST always with HYPOkalemia
- Can happen w/ ANY hyperthyroid state (Grave's most common)
- Classically seen in young men of Asian descent
Pathophysiology (see picture)
1. Rapid, exaggerated intracellular influx of potassium into muscles, mediated by increased
Na-K ATPase pumps (result of increased thyroid hormlone) --> Hypokalemia.
2. Thyroid hormone increase # and Sensitivity of Beta --> increased catecholamine mediated K uptake
3. Precipitants:
•Stressful events: --> increased adrenergic stimulation --> K uptake
•Hyperinsulinemia --> High carb meal --> insulin release --> K uptake
* predisposed patients seem to be more obese with increase insulin resistance
Clinical manifestations:
Can last minutes to days
Sudden onset flaccid muscle paralysis
Proximal > distal
Lower extremity > Upper extremity
+/- myalgias preceding
INFREQUENTLY: bulbar, ocular and respiratory muscles
Decreased or absent DTR
Rare complications: colonic pseudo-obstruction, acute hypercapnic respiratory failure and ventricular arrhythmia
EKG:
Cardiac conduction abnormalities (associated with hypokalemia): U waves, Wide QRS, prolonged QT, T wave flattening, heart block
Atrial arrhythmias (related to thyrotoxicosis)
Treatment:
- For Hypokalemia: replace, but cautiously
- Caveat: RELATIVE hypokalemia NOT a total body deficiency of K
Rebound HYPERkalemia often occurs
- No role in daily K supplements
- Rebound HYPERkalemia in up to 60% of patients
Recommend NO MORE than 90 mEq of K in 24 hours
OR
30 mEq K every 2 hours until improvement
OR
<10 mEq/ hour
- For Hyperthyroidism:
Methimazole vs PTU
Beta blockers – propranolol (20-40mg TID)
RAI therapy
- Avoid triggers
Excessive exercise
High carbohydrate foods
What else do you have to monitor?
Telemetry and serial EKG if abnormalities
Frequent potassium (?every 4 hours?)
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