Hi. I am a 47 yr old mum with a dx of Lupus/UCTD which has followed a steady path for many years. From 2012 I have started to have resp issues particularly severe when lying flat, sitting back, using my arms ie when cooking and in cold weather. Tests reveal a significantly weak diaphragm but cause unknown. I feel episodes of weakness from my neck down to my thighs, I have tested neg for MG & my SFEMG was 'unremarkable' although RNS 'showed decrement which seems a bit artefactual' however this has not been repeated. Now that the weather is colder again, I am revisiting the severe spasm/cramping I get in my thoracic, shoulder, hip & thigh area when I shiver. I am very prone to cold intolerance but this is painful & debilitating. These episodes will leave me struggling to breathe by the end of the day. I have had lots of thyroid tests, antibodies, CK, vitamin assays but nothing significant has been revealed. One test revealed low potassium - cause unknown. I took myself to an osteopath last week for help with relaxing my upper body musculature but was unable to tolerate lying flat so not hugely successful. The Drs acknowledge that I am having problems but feel that they have checked everything out so I am casting the net wider myself and would be so gratedful if anyone here has any thoughts..

Hope to hear back, Clare

P. I also find it hard sitting unsupported ie sitting on the floor and will have taut muscles and difficulty breathing

Type of Myotonia: Unsure if myotonia

Country: UK

Clare, there is a form of myasthenia which is associated with myotonia. You would not have the typical MG antibodies if you have a congenital form (and it can have later onset).
Congenital Myasthenic Syndromes

There is something called hypokalemic periodic paralysis which might be worth checking. It usually appears early in life, though, so your low level may have been a reaction. Are you taking any steroids? That can lower potassium.

Mitochondrial myopathies are very often associated with diaphragm weakness. They are usually inherited but may not appear until later in life. This is an overview...they are usually diagnosed by a neurologist specializing in metabolic disease (and usually they are only at children's hospitals):
Myopathies

Hope that gives you some things to investigate -

Jan

Type of Myotonia: Thomsen's

Country: US