Paramyotonia Congenita

Presenting Symptoms

Paramyotonia congenita (PC) can present with one of two problems (or a combo of both). The main thing with PC is to determine whether the patient is troubled by episodic weakness, myotonia, or both.

 

At the 2009 PPA Conference, some patients with suspected HyperKPP/PMC complained of muscle pain during and after attacks.

 

Therapy

Paramyotonia congenita (PC) can present with one of two problems (or a combo of both). The main thing with PC is to determine whether the patient is troubled by episodic weakness, myotonia, or both. The treatments for these two problems are different and if the patient has troubling symptoms with both, should be treated for both. One can treat the myotonia with Mexilitine as a first line agent (barring contraindications) and episodic weakness with Daranide or Diamox.

We continue to study PC and to make progress but this has not yet led to any new insights into NEW drugs that might help even more. This kind of advance always lags behind studies that help us understand the disease mechanism.

Mexiletine is very effective in preventing and reducing the degree of cold-induced stiffness and weakness. Some paramyotonia congenita patients have taken it for decades and still use it. Others take a single dose 2-3h prior to physical exercise in cold environment. The heart must be checked before administration.
Mexiletine is much more effective in sodium channel myotonia and paramyotonia than in chloride channel myotonia. The reason why is that it directly blocks the otherwise non-inactivating mutant sodium channels. Its use-dependent effect is of particular advantage as the non-inactivating channels high-frequently reopen.