Epidemiology:

-95 % of cases occur in men, usually young age (~20-39)
-Highest incidence in Asian descent but also seen in those of American Indians and Hispanic descent
-Any etiology of hyperthyroidism can be involved, but most commonly it is Grave’s disease
-Also exists in familial form (familial periodic paralysis)

Pathogenesis

-Thought to be a “channelopathy ” and thyroid hormone increases Na/K ATPase activity in skeletal muscle, driving potassium into the cell.
-High carb meals (more insulin release==>more shift of potassium into cells), ethanol, and over-exertion can trigger attack

Lab/Clinical features

-Proximal muscle weakness, with LE weakness>UE weakness, commonly presents in AM with inability to move lower extremities!
-Varying degrees of hypokalemia
-Mild hypomagnesemia, hypophosphatemia
-Elevated FT4, low TSH
-Elevated CK
-EKG with sinus tachycardia and often U waves (from hypokalemia)

DDX

1)Myasthenia Gravis (more sub-acute/chronic symptoms, more ptosis, bulbar weakness)
2)Botulism (hx of IVDU, black tar heroin, descending paralysis with CN paralysis and eye involvement)
3)GBS (2-4 weeks after GI illness, also ascending paralysis but with paresthesias and bulbar signs

Treatment

1)do NOT over-correct potassium as it can lead to rebound hyperkalemia!
2)Correct with ~10 meQ q1h KCL, check chem 7 q4h and MAX of 90 meQ/24 hour period
3)Treatment of Thyrotoxicosis with MMI and Propranolol (watch for agranulocytosis with MMI!)