Myotonic Dystrophy type 2 unmasked by physical activity resumption following COVID-19 lockdown: case discussion and review of the literature

Objective. Myotonic dystrophy type 2 (DM2; PROMM) is characterized by myotonia and muscle dysfunction, episodic muscle pain, proximal and axial weakness of the neck flexors. We describe the case of a young woman affected with a clinically silent form of DM2 disclosed by her return to physical exercise, a 7 km walk, after Covid-19 lockdown. Methods. The patient underwent neurological examination, serum CK dosage and electromyography after assessing the Emergency Room complaining of cramps and severe myalgia. Molecular screening for CNBP expansions was carried out on the patient and her family. Results. Clinical signs were generalized muscle weakness, more evident in the lower limb-girdle, myotonia at hands and foot fingers and dramatic elevation in CK levels. DM2 genetic assay revealed a pathological expansion in intron 1 of CNBP gene, confirming the clinical suspicion. Conclusions. The case we describe is the first, to our knowledge, addressing the impact of Covid pandemia on DM2 patients. In particular, we discuss the role of physical training in modulating the onset and the severity of clinical manifestations of DM2, since sustained regular exercise can mask the disease whereas prolonged suspension can cause massive muscle damage. Recent works investigate possible molecular mechanisms altered by forced physical inactivity, preventing skeletal muscle from adapting to the sudden, non-progressive training reactivation. Additional observations on DM2 patients, other myopathic subjects and elders will help clarify this important issue and provide useful behavioural advice.