Neurogenic disease with high CK: think muscle

HyperCKaemia is common in several myopathies but can accompany other disorders, including neuropathies. However, distinguishing neurogenic from myopathic hyperCKaemia is not always straightforward. A 58-year-old man had experienced muscle cramps and fatiguability since aged 3 years, with persistently high serum creatine kinase (CK). A positive family history prompted genetic testing for Charcot-Marie-Tooth disease type 1A, which was positive. However, his serum CK remained persistently high and neurological examination 17 years later identified diffuse muscle atrophy and weakness. Genetic testing for dystrophinopathy identified a novel missense variant on the DMD gene. Patients whose serum CK is in 'myopathic range', even those with definite neurogenic disease, should be investigated for additional myopathy, since this may require additional monitoring for pulmonary and cardiac complications.