Sporadic late-onset nemaline myopathy (SLONM): a rare observation of reversible heart damage

If nemaline-myopathies are well known to pediatricians because they are most often neonatal revelation or in the first months of life, it is not the same in adults where a very small contingent of patients is affected by a non-hereditary form  of the disease, with late onset of delicate diagnosis. This form, also identifiable by the acronym SLONM (for Sporadic Late Onset Nemaline Myopathy), results in a proximal and axial muscle deficit, quite rapidly progressive and disabling, and is very frequently accompanied, at a biological level, by a non-specific monoclonal gammopathy (or MGUS for monoclonal gammapathy of unknown significance). The positive diagnosis is based on the demonstration in the muscle of numerous rods (nemaline) by optical and electron microscopy. 

In an article published in December 2020, English clinicians report the original observation of a 65-year-old patient presenting for eighteen months a progressive muscle deficit of the lower limbs associated with a very significant muscle wasting in the thighs leading him to use a wheelchair. Almost at the same time, dyspneic syndrome appeared. The dosage of creatine phospho-kinases was in the standard. The diagnosis of SLONM was made on the presence of rods on the second of the biopsies the patient received, and the existence of a serum MGUS. Dyspnea has been reported in severe and progressive heart failure, treated by a drug therapy, subsequently supplemented by autologous stem cell transplantation. The patient was remarkably improved both cardiac and ambulatory. This observation confirms the rarity of cardiac complications in SLONM but also the beneficial nature of stem cell transplantation. 


Sporadic late-onset nemaline myopathy: a case report of a treatable cause of cardiac failure. C Turnquist, J C Grogono, M Hofer et al. Eur Heart J Case Rep. 2020 Dec 22;5(1):ytaa480.