(b).

Central causes

(i) Multiple sclerosis

(ii) Atypical Parkinson (PSP/MSA)

(iii) Stroke

(iv) Migraine

(v) Cerebellar disorders

(vi) Concussion

(vii) Medications

(viii) Psychogenic

(ix) Cardiovascular/Autonomic

PSP: progressive supranuclear palsy; MSA: multiple system atrophy.