ABSTRACT
Pure lower motor neurone syndromes A minority of patients (approximately 10%) present without upper motor neurone involvement. In the absence of typical features of ALS it is more difficult
to be certain of the diagnosis until upper motor neurone signs such as brisk reflexes or extensor plantars become evident. When the tempo of the disease is the same as for ALS with progression over months then the diagnosis can usually be made firmly. Overall, MND presenting as a pure lower motor neurone syndrome (termed progressive muscular atrophy) is more slowly progressive than full blown ALS. Regional variants where involvement remains confined to the lower or upper limbs respectively are described.11 Myasthenia gravis presenting with predominant bulbar weakness is occasionally misdiagnosed as ALS. High dose radiotherapy can lead to the appearance of a regional lower motor neurone syndrome up to 20 years after treatment.12
