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Corticomotoneuronal connections in primary lateral

sclerosis (PLS).

Weber M (No relation), H, Hirota N, Eisen A.

Neuromuscular Diseases Unit, Vancouver Hospital,

University of British Columbia, Canada.

markus.weber@...

Amyotroph Lateral Scler Other Motor Neuron Disord 2002

Dec;3(4):190-8

BACKGROUND: The relationship between primary lateral

sclerosis (PLS) and amyotrophic lateral sclerosis

(ALS) is uncertain. The slow progression and dominant

upper motor neuron features of PLS are associated with

a high threshold to cortical magnetic stimulation and

sometimes slow central motor conduction. In ALS the

cortical threshold may be reduced early in the disease

and central conduction is usually normal.

Corticomotoneuronal function appears to be impaired

differently in PLS and ALS.

SUBJECTS AND METHODS: We assessed corticomotoneuronal

function by analyzing the primary peak in the

peristimulus time histograms (PSTHs) in 12 PLS and 12

ALS patients. Surface recorded motor evoked potentials

(MEPs) and central motor conduction time (CMCT) were

determined. PSTHs were constructed from 4-5 different,

voluntarily recruited motor units in each patient and

the onset latency, number of excess bins, duration and

synchrony of the primary peak were measured.

RESULTS: The mean cortical threshold of single motor

units in PLS was 73.6%, significantly higher than in

ALS (60.3%; p < 2.2 x 10(-5)). Profoundly delayed

primary peaks occurred in both PLS and ALS. Onset

latency and desynchronization of the primary peak were

similar in PLS and ALS, but the duration of the

primary peak was significantly longer in PLS (p <

0.04).

CONCLUSIONS: Desynchronized primary peaks indicate

dysfunction or demise of corticomotoneurones. Higher

threshold and longer duration of the primary peak in

PLS probably reflect different excitability and

greater loss of corticomotoneuronal connections than

in ALS.