The prevalence of non-hereditary rod-shaped myopathy in adults is arguably underestimated

The nemaline-myopathies are well known to pediatricians because of a revelation most often neonatal or in the first months of life. However, it is also found in adults, who suffer from a non-hereditary form with late onset. This form is referred to by the acronym SLONM (for Sporadic Late Onset Nemaline Myopathy). It results in a proximal and axial muscle deficit, of varying severity and prognosis. The positive diagnosis is based on a range of clinical and biological arguments: the demonstration in the muscle of numerous rods (nemaline) and the detection of a monoclonal gammopathy (or MGUS for monoclonal gammopathy of unknown significance). 

In an article published in May 2021, English and Belgian clinicians report the discovery of ten cases of SLONM in a cohort of seventeen patients with a phenotype suggesting a LGMD but in whom high-throughput sequencing explorations ( in this case whole exome studies) were negative. The prevalence of SLONM could therefore be revised upwards. The authors also insist on the greater variety of clinical presentations, compared to the original description of this condition, and on the possible absence of associated MGUS. The lesions seen on the muscle biopsy, although not totally specific, remain key elements in the diagnosis. 


High prevalence of sporadic late-onset nemaline myopathy in a cohort of whole-exome sequencing negative myopathy patients. Willem De Ridder, Peter De Jonghe, Volker Straub, Jonathan Baets. Neuromuscul Disord. 2021 May 14; S0960-8966(21)00124-3