Por um site especializado em informações relacionadas à saúde para adultos mais velhos:
"...her tremulous voice and the persistent involuntary movement of her head, particularly during her performance in "On Golden Pond." These are classic symptoms of essential tremor that has affected the head and voice. She never appeared to have any difficulty walking. Ms. Hepburn did not have Parkinson's Disease, and despite her "disability," she was able to perform for many, many years."
Aqui está um excerto adicional de um Q & A do New York Times onde alguém perguntou " Por que Katharine Hepburn balançou a cabeça? ":
Katharine Hepburn's ailment, recently discussed on television by her niece Katharine Houghton, was not Parkinson's disease, but a progressive yet treatable neurological disorder called essential tremor. Ms. Hepburn's was referred to as familial tremor, the inherited form. Each child of a parent with the disease has a 50 percent chance of inheriting a gene that causes it. In other cases, there is no family history.
The disorder, which varies in location and severity, used to be called palsy. The International Essential Tremor Foundation, which offers information and helps search for a cure, says the disease stems from abnormal communication among areas of the brain, including the cerebellum, thalamus and brain stem. The group estimates that 10 million people in the United States and 200 million people worldwide have some form of the problem, often undiagnosed.
Many do not seek treatment because they fear Parkinson's or think tremors are part of aging. Shaking, usually starting with the hands, can begin at any age but is more common in older people; tremors starting with the head are more common in women.