Table 2

Differential diagnoses of skeletal muscle channelopathies

Myopathies–Pompe’s disease, myofibrillar myopathyMay have electrical myotonia on EMG.
Myopathies–metabolic, McArdle’s disease, RYR1 relatedEpisodic symptoms, often related to physical exertion, can be confused with periodic paralysis.
A specific RYR1/periodic paralysis overlap syndrome has recently been identified.
Becker muscular dystrophyLarge calves occasionally confused with calf hypertrophy seen in myotonia congenita.
Secondary causes of hypokalaemia for example, renal disease, drug inducedProfound hypokalaemia can induce muscle weakness in anyone, even without a genetic predisposition.
Thyrotoxic periodic paralysisCan present with hypokalaemic periodic paralysis, most commonly seen in Asian males. Essential to check thyroid function tests in all first presentations of hypokalaemic periodic paralysis as treatment of the thyrotoxicosis abolishes the episodes of periodic paralysis.
Migraine (hemiplegic migraine)Usually, there is a headache history to guide diagnosis but non-headache symptoms may predominate.
Paroxysmal movement disorders, for example, paroxysmal kinesigenic dyskinesia, GLUT1 deficiency, episodic ataxiaPatients may use the term ‘weakness’ erroneously when it is difficult to quantify a symptom
Functional disorderMost commonly a functional episodic weakness confused with periodic paralysis
  • EMG, electromyography.