A 66-year-old man reported an eight-year history of progressive ataxia and one-year
of weakness, fasciculation and muscle atrophy ([Figure 1]). Examination disclosed hypermetric saccades, diffuse fasciculations and absent
deep tendon reflexes. Family history was remarkable for autosomal dominant ataxia
([Figure 2]). MRI showed cerebellar atrophy. Genetic testing confirmed SCA3 (66 allelic expansion
on ATXN3 gene). EMG disclosed diffuse denervation and confirmed motor neuron disease
(MND).
Figure 1 Index patient with spinocerebellar ataxia type 3 and motor neuron disease presenting
with forearm flexor muscle atrophy (1A), split hand sign noted as a preferential wasting
of first dorsal interossei (1B) and thenar muscles abductor pollicis brevis (1C).
Brain MRI showed global diffuse atrophy, more marked on middle and superior cerebellar
peduncles, as on cerebellum (1D-E), and cervical spine MRI showed diffuse cervical
spinal cord atrophy with no signal changes (1F).
Figure 2 Heredogram. Family with spinocerebellar ataxia type 3 (SCA3).
Spinocerebellar ataxias (SCAs) may manifest as MND, particularly SCA2. Although SCA3
usually manifest as peripheral nerve involvement in a neuronopathy pattern and anterior
horn degeneration, marked MND is uncommon[1],[2]. SCA3 with simultaneous sporadic amyotrophic lateral sclerosis should also be considered
and may be related to accumulation of transactivation-responsive DNA-binding protein
43 (TDP-43) in the lower motor neurons[3].
