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Abstract
Objective To characterize and quantify peripheral nerve lesions and muscle degeneration in clinically, genetically, and electrophysiologically well-classified, nonpediatric patients with 5q-linked spinal muscular atrophy (SMA) by high-resolution magnetic resonance neurography (MRN).
Methods Thirty-one adult patients with genetically confirmed 5q-linked SMA types II, IIIa, and IIIb and 31 age- and sex-matched healthy volunteers were prospectively investigated. All patients received neurologic, physiotherapeutic, and electrophysiologic assessments. MRN at 3.0T with anatomic coverage from the lumbosacral plexus and proximal thigh down to the tibiotalar joint was performed with dual-echo 2D relaxometry sequences with spectral fat saturation and a 3D T2-weighted inversion recovery sequence. Detailed quantification of nerve injury by morphometric and microstructural MRN markers and qualitative classification of fatty muscle degeneration were conducted.
Results Established clinical scores and compound muscle action potentials discriminated well between the 3 SMA types. MRN revealed that peroneal and tibial nerve cross-sectional area (CSA) at the thigh and lower leg level as well as spinal nerve CSA were markedly decreased throughout all 3 groups, indicating severe generalized peripheral nerve atrophy. While peroneal and tibial nerve T2 relaxation time was distinctly increased at all analyzed anatomic regions, the proton spin density was clearly decreased. Marked differences in fatty muscle degeneration were found between the 3 groups and for all analyzed compartments.
Conclusions MRN detects and quantifies peripheral nerve involvement in SMA types II, IIIa, and IIIb with high sensitivity in vivo. Quantitative MRN parameters (T2 relaxation time, proton spin density, CSA) might serve as novel imaging biomarkers in SMA to indicate early microstructural nerve tissue changes in response to treatment.
Glossary
- ALSFRS-R=
- Amyotrophic Lateral Sclerosis Functional Rating Scale–Revised;
- ANOVA=
- analysis of variance;
- CMAP=
- compound muscle action potential;
- CSA=
- cross-sectional area;
- HFMSE=
- Hammersmith Functional Motor Scale–Expanded;
- LUN=
- left ulnar nerve;
- MR=
- magnetic resonance;
- MRN=
- magnetic resonance neurography;
- NeuroNEXT=
- Network for Excellence in Neuroscience Clinical Trials;
- PN=
- peroneal nerve;
- PNS=
- peripheral nervous system;
- PNP=
- peripheral neuropathy;
- RMN=
- right median nerve;
- RULM=
- Revised Upper Limb Module;
- SMA=
- spinal muscular atrophy;
- SMN=
- survival motor neuron;
- SN=
- spinal nerve;
- SNAP=
- sensory nerve action potential;
- SNR=
- signal-to-noise ratio;
- SPACE=
- sampling perfection with application-optimized contrasts using different flip angle evolution;
- TE=
- echo time;
- TN=
- tibial nerve
Footnotes
Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
- Received January 20, 2019.
- Accepted in final form March 21, 2019.
- © 2019 American Academy of Neurology
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