What are the key clinical features to differentiate between primary and secondary dystonia in a patient?

Key clinical features differentiating primary from secondary dystonia include onset, distribution, associated neurological signs, and progression. Primary dystonia typically presents with an insidious onset, often in childhood or young adulthood, and usually manifests as isolated dystonia without other neurological abnormalities. It often starts focally (e.g., in a limb or the neck) and may generalize over time but lacks additional neurological signs such as weakness or sensory loss NICE NG127 Albanese 2003. In contrast, secondary dystonia usually has a later onset and is associated with identifiable causes such as brain injury, exposure to drugs, metabolic disorders, or neurodegenerative diseases. It often presents with additional neurological features including pyramidal signs, cognitive impairment, or sensory deficits, and the dystonia distribution may be more complex or segmental NICE NG127 Schneider & Bhatia 2009.

Additional clinical clues favoring secondary dystonia include a history of precipitating factors (e.g., trauma, infection, or medication), rapid progression, and poor response to typical dystonia treatments. Functional dystonia, a subtype of secondary dystonia, may show inconsistency in symptoms, distractibility, and variability over time, which helps differentiate it from primary dystonia Frucht et al. 2020. Neuroimaging and laboratory investigations often reveal underlying structural or metabolic abnormalities in secondary dystonia, whereas primary dystonia usually shows normal imaging NICE NG127 Schneider & Bhatia 2009.