the spinocerebellar ataxias ( scas ) are a group of genetically heterogeneous neurodegenerative disorders characterized by cerebellar , pyramidal , extrapyramidal , cognitive , and peripheral nerve dysfunction in variable combination .
dystonia can be encountered in a small subset of patients with sca , but task - specific dystonia ( writer 's cramp ) is extremely rare and has been reported only in association with stray cases of sca types 6 , 7 , and 14 worldwide .
we report a rare case of genetically confirmed sca type 1 ( sca1 ) with a prominent and disabling writer 's cramp .
a 48-year - old , nonalcoholic , male police officer , presented to us with 2 years history of very slowly progressive dysarthria and a mild gait imbalance noticed only during running and marching . for the past 4 months , he also complained of an abnormal posturing and stiffness of his right hand while writing . there was no abnormal posturing of the hand , or any other part of the body while carrying out any other activities of daily living . there was no history of any motor or sensory deficit or incoordination of the upper limbs . his history was insignificant and there was no history of a similar illness in his siblings or other family members . on examination ,
his higher mental functions were preserved and cranial nerves were intact . on motor examination ,
there was no nystagmus , but a slight slowing of the horizontal and vertical saccades was observed .
there was no incoordination in the upper limbs , but the heel - shin test was slightly impaired .
a task - specific dystonia in the form of a writer 's cramp with lifting of the right index finger off the pen and curling of the thumb and the last two digits was documented while writing .
there was no evidence of dystonia at rest or extrapyramidal manifestations such as bradykinesia , rigidity , or tremor in any other part of the body . in view of the history of a very mild , slowly progressive ,
cerebellar ataxia of long duration , slow saccades , hyperreflexia and a prominent writer 's cramp , a possibility of inherited sca with task - specific dystonia was kept .
his routine investigations including hemogram , blood sugar , liver , renal , thyroid function tests , and serum vitamin b12 levels were all normal .
he tested negative for antibodies to hiv , hepatitis c virus , and hepatitis b surface antigen .
magnetic resonance imaging brain revealed significant cerebellar hemispheric and vermian atrophy [ figure 1 ] .
his writer 's cramp responded well to botulinum toxin injection with a significant improvement in his handwriting [ figure 2 ] .
t1 axial and t2 coronal magnetic resonance imaging brain images showing cerebellar hemispheric and vermian atrophy handwriting specimen before ( a ) and after ( b ) botulinum toxin injection
dominantly inherited scas are a heterogeneous group ( 40 and counting ) of neurodegenerative disorders identified by specific mutations .
they predominantly affect the cerebellum and its connections and are characterized by prominent limb ataxia with impaired balance , gait , speech , and eye movements .
movement disorders in the form of myoclonus , chorea , parkinsonism , tremors , and dystonia have also been described .
dystonia is commonly seen only in sca types 17 , 3 , and 2 . however , there are case reports of both focal and generalized dystonia in sca types 1 , 6 , 7 , 8 , 12 , 14 , 20 , and 36 as well .
sca1 is associated with abnormal cytosine - adenine - guanine repeats on the ataxin 1 gene on chromosome 6 and can be accompanied by cognitive dysfunction , parkinsonism , and dystonia in addition to ataxia
. however , extrapyramidal features are more common in sca types 2 and 3 than sca1 .
studied extrapyramidal manifestations in 85 patients of sca types 1 , 2 , and 3 .
overall dystonia was encountered in 13 of the 85 ( 15.2% ) cases only and was more common in sca2 ( 17.9% , n = 5/28 ) and sca3 ( 17.6% , n = 3/17 ) than sca1 ( 12.5% , n = 5/40 ) . in a study by lee et al .
, extrapyramidal symptoms were found in 53% sca3 ( n = 29 ) and 12% sca2 patients ( n = 17 ) .
none of the 6 cases with sca1 had any evidence of extrapyramidal dysfunction in their cohort .
found dystonia in only 9.1% ( n = 33 ) of cases of sca1 as compared to 44.4% ( n = 9 ) cases of sca2 .
in contrast to the usual pattern of focal or generalized dystonia reported in sca1 , our case presented with a prominent task - specific dystonia in the form of a writer 's cramp and added to the clinical spectrum of this subtype .
a review of the literature reveals that even in the sca subtypes manifesting with dystonia , task - specific dystonia such as writer 's cramp is extremely rare .
there are only stray case reports of writer 's cramp in sca types 6 , 7 , and 14 from all over the world [ table 1 ] and no reported case of this association in sca1 , as observed in our case .
summary of reported cases of task specific dystonia in spinocerebellar ataxias pathways implicated in the manifestation of dystonia include the cerebello - thalamocortical and basal ganglia - thalamocortical circuits . in a pathoanatomical study of patients with sca1 , rb et al
. found neuronal loss and degeneration in these pathways besides the primary motor cortex and cerebellum .
it was also seen that the extent of the involvement of these structures correlated well with predominant clinical symptoms that were seen in an individual case .
drr et al . have observed that the basal ganglia , especially the internal pallidum and the subthalamic nucleus show severe degeneration in sca3 but are relatively spared in sca1 which may account for the more frequent dystonia in sca3 .
in sca patients with writer 's cramp , the dystonia can precede , accompany or follow the onset of cerebellar ataxia . in our patient ,
writer 's cramp manifested almost 1 years after the onset of the gait ataxia but subsequently became the most prominent and disabling complaint . to the best of our knowledge ,
this is probably the first case report of sca1 with a task - specific dystonia or writer 's cramp .
our case highlights the ever - expanding phenotypic heterogeneity of the sca 's in general and sca1 in particular .
 dystonia can be encountered in a small subset of patients with spinocerebellar ataxia ( sca ) , but task specific dystonia is extremely rare . 
 we report a case of a 48-year - old male with confirmed sca type 1 ( sca1 ) with mild progressive cerebellar ataxia and a prominent and disabling writer 's cramp . 
 this case highlights the ever - expanding phenotypic heterogeneity of the sca 's in general and sca1 in particular . 