HPI: 35 yo hispanic M with history of gout and HTN, presents with acute onset generalized weakness, particularly pronounced in b/l upper and lower extremities. 

• Symptoms started abruptly last night after a strenuous and stressful work day
• No change in mental status
• No recent illness, insect bites or rashes
• Denies tremor, weight change, anxiety

Physical Exam:

• Vitals WNL
• Weakness most pronounced in proximal muscles, with legs slightly weaker than arms Grip strength preserved
• Normal reflexes

DDx:

• Thyrotoxic periodic paralysis
• Hypokalemic periodic paralysis
• Myasthenic crisis
• Guillain-Barre syndrome
• Transverse myelitis
• Tick paralysis

Initial Orders:

• CBC, BMP, Thyroid panel (TSH, Free T3, Free T4), CK, Mag, Phos
• EKG

Results and clinical course:

• K: 1.7
• Mag: 1.5
• TSH < 0.01
• Free T4: 5.9
• T3, Free: 23.5
• EKG: NSR with sinus arrhythmia and prolonged QTc

Management:

• Replete with PO and IV potassium and IV magnesium
• Symptoms began to improve rapidly with potassium replacement
• Admit to telemetry monitored bed for at least 24h and check serial BMPs to monitor for rebound hyperkalemia
• Patient started on methimazole for hyperthyroid

Teaching points:

• Thyrotoxic periodic paralysis is a form of acquired hypokalemic periodic paralysis, often precipitated by rest after strenuous exercise or high carb load
• Treat with KCl, continuous cardiac monitoring and monitor K levels for rebound hyperkalemia
• For acute weakness not responsive to potassium replacement, use Propranolol
• Treat hyperthyroidism - attacks should cease with euthyroid state

References:

Chaudhry MA, Wayangankar S. Thryotoxic Periodic Paralysis: A concise review of the literature. Curr Rheumatol Rev. 2016;12(3):190-194.

Kung AW. Clinical review: Thyrotoxic periodic paralysis: a diagnostic challenge. J Clin Endocrinol Metab. 2006 Jul;91(7):2490-5. Epub 2006 Apr 11.

Vijayaumar A, Ashwath G, Thimmappa D. Thyrotoxic periodic paralysis: clinical challenges. J Thyroid Res 2014;2014:649502