Since 1986 interferon alpha has been a mainstay of hepatitis C therapy. Interferons consist of a group of cytokines that activate antiviral responses in the body’s immune cells. Depression, irritability, and impaired concentration are all well-known neuropsychiatric adverse events of interferons. However, a rarely noted and reported on interferon-related event is parkinsonism.

A recent report published in Clinical Neuropharmacology examined two case studies of parkinsonism onset which proceeded alpha interferon use; the authors also looked into 10 other reports of interferon-associated parkinsonism in literature.

The first case study centers on a 51-year-old male engineer who was initially evaluated for tremor in 2007. His history included chronic hepatitis C genotype 1a, with corrhosis and migraine headaches with family history of multiple sclerosis (mother). He was first treated for hepatitis C from 1994 to 1995 with interferon alpha-2b, with no response. He later received a combination treatment of interferon alpha-2b and ribavirin, but this too resulted in no response. He finally achieved sustained virologic response in 2001 with a triple therapy regimen (interferon alpha-2b + ribavirin + amantadine for 36 weeks). During treatment in 2001, it was noted that the patient had developed an intermittent rest and postural tremor and restless legs. No parkinsonism tremor was noted in a 2003 examination, 10 months after the treatment ended.

However, in 2006 he experienced tremors which lasted for approximately 1 year. This manifested itself in intermittent shaking of his right hand, and general diminishing of motor skill and stiffness in his his right hand (his ‘good’ hand), some slowing of cognitive processing and a reduction in volume and speed of voice. Upon examination in 2007, the patient showed normal attention, concentration, and language, but modest degree of reduced spontaneity of facial expression. His physical exam revealed a bilateral low-amplitude postural and end-of-reach kinetic tremor; this was diagnosed as idiopathic Parkinson’s disease (PD), Hoehn and Yahr stage I.