Periodic paralysis must be distinguished from other conditions.
Differential diagnosis may include:
(1) seizure disorder
(2) metabolic myopathy such as McArdle's disease
(3) vascular disorder
(4) syncope
When to consider another diagnosis:
(1) fluctuation of fixed weakness rather than attacks of weakness
(2) absence of myotonia on cooling OR weakness with exercise
(3) cramps with myoglobinuria
(4) altered consciousness
(5) rhythmic jerking
(6) cranial nerve symptoms
(7) pre-syncopal symptoms
(8) pain or numbness
Finding |
Type of Periodic Paralysis (PP) |
low serum TSH (hyperthyroidism) |
thyrotoxic hypokalemic PP |
cardac arrhythmia or long QT on ECG |
Andersen-Tawil Syndrome |
dysmorphic features |
Andersen-Tawil Syndrome |
onset with cooling |
paramyotonia congenital (PC) |
myotonia clinically or on EMG |
presence suggests paramyotonia congenital or hyperkalemic PP; absence suggests hypokalemic PP |
If a periodic paralysis is suspected, then consider the following in making the diagnosis:
(1) age at onset
(2) serum potassium
(3) frequency
(4) severity and duration of attacks
Parameter |
Paramyotonia PC |
Hyperkalemic PP |
Hypokalemic PP |
age at onset |
infancy |
< 10 years |
5 to 20 years |
serum potassium |
normal |
high or normal |
low |
frequency |
frequent |
frequent |
infrequent |
severity/duration |
less and < 24 hours |
less and < 24 hours |
severe and > 24 hrs |
Specialty: Surgery, orthopedic
ICD-10: ,