Motor unit remodelling in multifocal motor neuropathy: The importance of axonal loss

Nidhi Garg; James Howells; Con Yiannikas; Steve Vucic; Arun V Krishnan; Judith Spies; Hugh Bostock; Emily K Mathey; John D Pollard; Susanna B Park; Matthew C Kiernan

doi:10.1016/j.clinph.2017.07.414

Motor unit remodelling in multifocal motor neuropathy: The importance of axonal loss

Clin Neurophysiol. 2017 Oct;128(10):2022-2028. doi: 10.1016/j.clinph.2017.07.414. Epub 2017 Aug 7.

Authors

Nidhi Garg¹, James Howells², Con Yiannikas³, Steve Vucic⁴, Arun V Krishnan⁵, Judith Spies⁶, Hugh Bostock⁷, Emily K Mathey⁸, John D Pollard⁹, Susanna B Park¹⁰, Matthew C Kiernan¹¹

Affiliations

¹ Brain and Mind Centre, Sydney Medical School, The University of Sydney, 94 Mallett St, Camperdown, NSW 2050, Australia; Department of Neurology, Royal Prince Alfred Hospital, The University of Sydney, NSW, Australia. Electronic address: nidhi.garg@sydney.edu.au.
² Brain and Mind Centre, Sydney Medical School, The University of Sydney, 94 Mallett St, Camperdown, NSW 2050, Australia. Electronic address: james.howells@sydney.edu.au.
³ Department of Neurology, Concord and Royal North Shore Hospitals, The University of Sydney, NSW, Australia. Electronic address: y.con@bigpond.com.
⁴ Departments of Neurology and Neurophysiology, Westmead Hospital, The University of Sydney, NSW, Australia. Electronic address: s.vucic@neura.edu.au.
⁵ Prince of Wales Clinical School, University of New South Wales, NSW, Australia. Electronic address: arun.krishnan@unsw.edu.au.
⁶ Brain and Mind Centre, Sydney Medical School, The University of Sydney, 94 Mallett St, Camperdown, NSW 2050, Australia; Department of Neurology, Royal Prince Alfred Hospital, The University of Sydney, NSW, Australia. Electronic address: jmspies@tpg.com.au.
⁷ MRC Centre for Neuromuscular Diseases, National Hospital for Neurology and Neurosurgery, Queen Square, London, United Kingdom; Institute of Neurology, University College London, United Kingdom. Electronic address: h.bostock@ucl.ac.uk.
⁸ Brain and Mind Centre, Sydney Medical School, The University of Sydney, 94 Mallett St, Camperdown, NSW 2050, Australia. Electronic address: emily.mathey@sydney.edu.au.
⁹ Brain and Mind Centre, Sydney Medical School, The University of Sydney, 94 Mallett St, Camperdown, NSW 2050, Australia; Department of Neurology, Royal Prince Alfred Hospital, The University of Sydney, NSW, Australia. Electronic address: john.pollard@sydney.edu.au.
¹⁰ Brain and Mind Centre, Sydney Medical School, The University of Sydney, 94 Mallett St, Camperdown, NSW 2050, Australia. Electronic address: susanna.park@sydney.edu.au.
¹¹ Brain and Mind Centre, Sydney Medical School, The University of Sydney, 94 Mallett St, Camperdown, NSW 2050, Australia; Department of Neurology, Royal Prince Alfred Hospital, The University of Sydney, NSW, Australia. Electronic address: matthew.kiernan@sydney.edu.au.

PMID: 28837908
DOI: 10.1016/j.clinph.2017.07.414

Abstract

Objective: To estimate the degree of axonal loss in patients diagnosed with multifocal motor neuropathy (MMN) using a novel assessment of motor unit numbers and size.

Methods: Automated motor unit number estimation using a compound muscle action potential (CMAP) scan was undertaken in median nerves with conduction block. Results were compared with 30 age-matched healthy controls.

Results: Compared with healthy controls, MMN patients had fewer motor units (MMN: 33±11vs HC: 93±36 [mean±SD]; p<0.0001) and larger 'size of the largest unit' (MMN: 1.2±0.5mVvs HC: 0.4±0.1mV; p<0.0001), despite having normal distal CMAP amplitudes (MMN: 7.6±1.8mVvs HC: 8.7±2.5mV; p=0.24).

Conclusions: MMN is associated with marked axonal loss which may be masked by striking re-innervation resulting in preservation of distal CMAP amplitudes.

Significance: Assessment of motor unit properties should be incorporated into assessment of disease progression in MMN, given that nerve conduction studies are insensitive to motor unit remodelling.

Keywords: Autoimmune diseases; Axonal degeneration; Multifocal motor neuropathy; Neuromuscular disease; Neurophysiology.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Action Potentials / physiology
Adult
Aged
Axons / physiology*
Cohort Studies
Female
Humans
Male
Middle Aged
Motor Neuron Disease / diagnosis
Motor Neuron Disease / physiopathology*
Nerve Degeneration / diagnosis
Nerve Degeneration / physiopathology*
Neural Conduction / physiology
Polyneuropathies / diagnosis
Polyneuropathies / physiopathology*
Prospective Studies
Recruitment, Neurophysiological / physiology*