Myotonia Congenita is a rare neuromuscular disease manifest by “painful muscle cramps or myalgia as well as transient muscle weakness following myotonic stiffness”. Article describes 2 cases – one that got worse with pregnancy which is what Fibromyalgia also does. The transient weakness after cramping can be easily missed though EMG does pick up the problem.
J Clin Neurol. 2015 Apr;11(2):188-91. doi: 10.3988/jcn.2015.11.2.188.
The Overlap between Fibromyalgia Syndrome and Myotonia Congenita.
Nam TS(1), Choi SY(2), Park DJ(3), Lee SS(3), Kim YO(4), Kim MK(5).
- muscle disorder
- sarcolemmal hyperexcitability with mutations in chloride ion channel
- 2 forms – autosomal-dominant myotonia and recessive generalized myotonia
- “painful muscle cramps or myalgia as well as transient muscle weakness following myotonic stiffness”
- pain and stiffness “worsened by emotional stress, cold exposure,
sleep disturbance, dietary habit, excessive physical activity, and pregnancy.”
- Needle EMG and genetic testing confirm
Case 1 – 31 yr old typical FM except:
- “had a history of transient muscle weakness lasting for periods of no more than several seconds in her legs when she suddenly had to walk at a pedestrian crossing or a bus stop.”
- Moderate muscular hypertrophy was seen on exam.
- positive EMG and genetics despite negative Fhx
- used sodium channel blockers (lacosamide or carbamazepine) and amitriptyline.
Case 2 – 37 yr old male with widespread pains and depression except:
- Male (my comment)
- Pain 8/10
- “cold-water testing aggravated the muscle stiffness and cramps in his forearm.”
- transient muscle weakness in childhood only
- sister episodic transient muscle weakness
- No meds successful
Comment – tough one. Presence of family history, muscle cramps followed by transient weakness, FM in a male, muscular hypertrophy, pain more severe and not necessarily responsive to treatments all are hints for Myotonia Congenita. EMG done for muscle cramps could confirm it. I wrote about how myotonic dystrophy type II can be confused with fibromyalgia:
Fibromyalgia (FM) Tragic Misdiagnosis – Myotonic Dystrophy Type 2 and Cervical Spinal Stenosis – New Treatments as Result