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Weak in the Flexors - FMLH NR 6/21/19 - Dr. Kristiansen

Updated: Aug 6, 2019

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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