Long-term Follow-up of Monomelic Amyotrophy of the Upper Limb

I read with great interest the article by Van den Berg-Vos et al¹ that described a prospective study of 32 patients with lower motor neuron syndrome with duration of disease of 4 years or more who were followed up for 72 months to identify the group of patients who have either slow progression or attain a stationary course for many years and do not progress to having amyotrophic lateral sclerosis. The authors describe a favorable prognosis in 8 patients with segmental distribution of muscle involvement. No significant change in muscle strength was observed but there was spread to adjoining segments in one patient and to contralateral side in another.

In this context, I wish to draw attention to 2 articles; the first is by Barontini et al² from Italy and included 3 patients with focal amyotrophy who were followed up clinically and neurophysiologically for 13 to 15 years and whose disease course remained stationary after an initial progressive course of 2 years. The second is our long-term follow-up study³ of 44 patients from India with monomelic amyotrophy of the upper limb with illness duration of 5 years or more, with the objectives to determine whether (1) atrophy and weakness progresses beyond this period, (2) the illness spreads to the other limbs and (3) the disease progresses to amyotrophic lateral sclerosis. The clinical features of monomelic amyotrophy have been described, and the essential features are focal atrophy of muscles of upper limb in adults, mainly restricted to the C8 to T1 segments, although in a few patients, proximal muscles may be involved with no evidence of upper motor neuron signs.^{4 - 5} Our study was prospective, with a mean follow-up period of 9.7 years.³ The salient findings were absence of progression of atrophy and weakness in the affected limb for more than 5 years, with the exception of 2 patients in whom there was progression for 6 years in one patient and 8 years in another, with a subsequent stationary course. In 7 patients, at presentation, there was mild clinical involvement or neurogenic changes on electromyography of the contralateral limb; however, there was gross asymmetry between the two limbs. During follow-up, 1 additional patient developed mild atrophy and weakness in the contralateral limb. There was no progression to the lower limbs in all the 44 patients and, reassuringly, none progressed to develop upper motor signs or amyotrophic lateral sclerosis.

The observations of Van den Berg-Vos RM et al¹ on the natural history of segmental distal muscular atrophy are similar to Barontini and colleagues’² and our³ findings in patients with monomelic amyotrophy, which is also a segmental muscular atrophy.

Correspondence: Dr Gourie-Devi, Department of Neurology, Institute of Human Behaviour and Allied Sciences, Dilshad Gardens, New Delhi 110095, India (mgouriedevi@gmail.com).

Financial Disclosure: None reported.