BACKGROUND: Dystonia is a movement disorder characterized by involuntary muscle 
contractions that cause twisting movements and abnormal postures. Primary 
dystonia is the most common form and is thought to be a multifactorial condition 
in which one or more genes combine with environmental factors to reach disease.
METHODS: We reviewed controlled studies on possible environmental risk factors 
for primary early- and late-onset dystonia.
RESULTS: Environmental factors associated with primary early-onset dystonia are 
poorly understood. Early childhood illnesses have been reported to be more 
frequent in patients with DYT1 dystonia than in subjects carrying the DYT1 
mutation that did not manifest dystonia, thus raising the possibility that such 
exposures precipitate dystonia among DYT1 carriers. Conversely, several 
environmental factors have been associated with primary adult-onset focal 
dystonias compared to control subjects. Namely, eye diseases, sore throat, 
idiopathic scoliosis, and repetitive upper limb motor action seem to be 
associated with blepharospasm (BSP), laryngeal dystonia (LD), cervical dystonia 
(CD), and upper limb dystonia, respectively. In addition, an inverse association 
between coffee drinking and BSP has been observed in both case-unrelated control 
and family-based case-control studies. Additional evidence supporting a causal 
link with different forms of primary late-onset dystonia is only available for 
diseases of the anterior segment of the eye, writing activity, and coffee 
intake.
CONCLUSION: There is reasonable epidemiological evidence that some environmental 
factors are risk-modifying factors for specific forms of primary adult-onset 
focal dystonia.