Cause:Familial periodic paralysis (FPP) is inherited; unknown in other two
Pathophys:"Channel-opathies". Hyperkalemic myopathy (HyperK) may be mediated through an aldosterone-like steroid intermittently secreted
Sx:Paralysis, intermittent, periodic, often precipitated by exercise or, in HyperK, insulin
Si:Flaccid paralysis
Death due to cardiac arrhythmias and respiratory impairments especially; PVCs and ventricular tachycardia (Nejm 1972;286:253)
If K+ elevated, r/o rare hypoaldosterone syndrome probably due to absent renin (Nejm 1972;287:573)
Lab: Path:Muscle biopsy shows clear vacuoles throughout muscle, intracellular "focal hydropic changes," often PAS-positive (glycogen)
Renal biopsy shows similar vacuoles at base of tubular cells
Rx:
of FPP, rx of hypo/hyper K+
of normo- or hyperkalemic myopathy, acetazolamide 125-250 mg po bid (Ann IM 1977;86:169) probably works by increasing K+ loss by blocking H+ secretion
of HypoK, K+ iv, or po acetazolamide 125-250 mg po bid which works by causing an acidosis and thereby driving K+ up; or more likely, inhibits an aldosterone-like steroid (Ann IM 1970;73:39; Nejm 1968;278:582)