Differential diagnoses of skeletal muscle channelopathies
| Diagnosis | Comment |
| Myopathies–Pompe’s disease, myofibrillar myopathy | May have electrical myotonia on EMG. |
| Myopathies–metabolic, McArdle’s disease, RYR1 related | Episodic 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 dystrophy | Large calves occasionally confused with calf hypertrophy seen in myotonia congenita. |
| Secondary causes of hypokalaemia for example, renal disease, drug induced | Profound hypokalaemia can induce muscle weakness in anyone, even without a genetic predisposition. |
| Thyrotoxic periodic paralysis | Can 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 ataxia | Patients may use the term ‘weakness’ erroneously when it is difficult to quantify a symptom |
| Functional disorder | Most commonly a functional episodic weakness confused with periodic paralysis |
EMG, electromyography.