Abstract Details

Title Predicting benign brachial monomelic amyotrophy: factors at presentation that differentiate from amyotrophic lateral sclerosis

Topic Neuromuscular and Clinical Neurophysiology (EMG)

Presentation(s) P1 - Poster Session 1 (5:30 PM-6:30 PM)

Poster/Presentation
Number 12-016

Objective To determine the diagnostic value of clinical features and investigations at onset
that differentiate amyotrophic lateral sclerosis (ALS) from benign brachial monomelic
amyotrophy (BMA).

Background BMA, a term sometimes used interchangeably with Hirayama or Sobue disease,
is a rare syndrome characterised by isolated lower motor neurone weakness of the upper
limbs, which can mimic ALS at onset. In contrast to ALS, following a period of slow
progression, the symptoms of BMA arrest. Differential diagnosis can be challenging at first
presentation.

Design/Methods Detailed phenotyping of baseline clinical profiles, biochemical, imaging
and electrophysiological findings was performed in patients with isolated upper-limb onset
weakness, presenting to a tertiary neuroscience centre over 15 years in a retrospective
study. Final diagnosis after >5 years of follow-up was recorded. Multivariate logistic regression
was used to develop a predictive model.

Results Compared to the ALS group (n=45), patients with BMA (n=13) were significantly
younger (median 39 years (20-50) vs 64 years (53-70), p<0.0001) and had a longer duration
of symptoms (median 53 months (28-100) vs 18 months (10-47), p=0.013) at presentation.
Clinically, BMA patients more frequently presented with unilateral onset (p=0.016), distal
weakness (p=0.024), fewer clinical fasciculations (p<0.0001), sensory abnormalities
(p=0.038), and less frequent electrophysiological denervation outside the cervical region
(p=0.0002), compared to ALS patients. The optimised predictive model simply combined age
at symptom onset with the presence of fasciculations in any region, and correctly predicted
93.0% of BMA and ALS diagnoses (sensitivity for diagnosis of BMA: 76.9%; specificity 97.7%).

Conclusions Clinical and electrophysiological differences at presentation can help
differentiate between upper-limb onset ALS and BMA. Young age at onset and absence of
clinical fasciculations may support a diagnosis of BMA rather than ALS in patients presenting
with isolated upper limb weakness. The predictive model now needs to be validated in an
independent cohort.

Authors/Disclosures
Sona Mistry, MD, MBBS PRESENTER	No disclosure on file
	No disclosure on file
	No disclosure on file
Christopher McDermott	The institution of Christopher McDermott has received research support from NIHR. The institution of Christopher McDermott has received research support from Motor Neurone Disease Association.
Pamela J. Shaw, MD, FRCP, FAAN (The University of Sheffield, Sheffield Inst for Translational Neurosc)	No disclosure on file
	No disclosure on file

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