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Natural history of SMA IIIb

Muscle strength decreases in a predictable sequence and magnitude

From the Department of Neurology (F.D., P.S., Y.P.), Istanbul Medical Faculty, and Department of Genetics (M.P.), Institute of Experimental Medical Research, Istanbul University, Turkey.

Address correspondence and reprint requests to Dr. Feza Deymeer, Department of Neurology, Istanbul Medical Faculty, Istanbul University, Capa 34390, Istanbul, Turkey deymeer{at}istanbul.edu.tr

Objective: To assess the natural progression of muscle weakness in spinal muscular atrophy (SMA) IIIb.

Methods: Ten patients with SMA IIIb were followed for at least 10 years. Age at disease onset varied between 9 and 18 years. Patients were initially seen 2 to 10 years after disease onset. They were evaluated at approximately 2, 5, 10, 15, and 20 years of disease duration depending on the timing of their initial visit after onset. Medical Research Council (MRC) scale was used with particular attention to proximal muscles.

Results: The MRC grade declined with years in all of the muscles. The decline was usually not more than by one MRC grade for each 5-year period. There were 5–10 year periods when some muscles appeared to remain stationary. The succession of weakness was first triceps, then biceps and deltoid for upper extremity muscles and first thigh adductors, then iliopsoas, then quadriceps femoris, then hamstrings, thigh abductors, and gluteus maximus for lower extremity muscles. There was a remarkable uniformity between patients in the MRC grade for each muscle at each stage: in the first 5 years of the disease, triceps, iliopsoas, thigh adductors, and quadriceps femoris were the muscles which had noticeable weakness.

Conclusions: These findings show that strength in spinal muscular atrophy IIIb decreases over time, explaining the progressive functional loss. The sequence of weakness in the lower extremities suggests that the disease starts segmentally involving the upper lumbar segments of the medulla spinalis initially. The slowness of the deterioration may have implications for clinical trials.

Abbreviations: GMFT = Gross Motor Function Test; LE = lower extremities; MRC = Medical Research Council; SMA = spinal muscular atrophy; SMN1 = survival motor neuron gene; UE = upper extremities.

Supported by the Istanbul University Research Fund.

Disclosure: The authors report no disclosures.

Presented as a poster at the World Muscle Society meeting, Giardini Naxos, 2007.

Received January 27, 2008. Accepted in final form May 21, 2008.

This article has been cited by other articles:

				S. Piepers, W. -L. van der Pol, F. Brugman, J.H.J. Wokke, L. H. van den Berg, F. Deymeer, P. Serdaroglu, Y. Parman, and M. Poda NATURAL HISTORY OF SMA IIIb: MUSCLE STRENGTH DECREASES IN A PREDICTABLE SEQUENCE AND MAGNITUDE Neurology, June 9, 2009; 72(23): 2057 - 2058. [Full Text] [PDF]

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