Singer Carly Simon has been diagnosed with Parkinson's disease but says she won't be defined by her illness and is releasing a new album. "So many people have written to me, kindly wondering about my relative silence, asking how I am and what I have been doing," she said in a statement."The truth is, I've been learning how to live with Parkinson's disease."Carly Simon's biggest hit was You're So Vain, released in 1972. (Supplied: Wiki Commons)Declining mobilityThe singer, 83, had been experiencing arthritis in one of her hips and both her knees and had replacement surgeries for those three joints. But her mobility continued to decline. At times, she said, she could not walk without "considerable help".Simon said she and her family knew "something more was going on" and after an extensive evaluation, she was diagnosed with Parkinson's."It has taken me some time to understand the diagnosis, to adjust to it, and to decide how much I wanted to say about it publicly," she said."Parkinson's is different for everyone and it can be unpredictable. "Some days I'm so tired I can't get the day moving at all. On others, it gives me a little more room to move, think, work, and feel like myself."Tremors, stiffness and slurred speechParkinson's is a neurological disease that robs people of control over their movements. It typically starts with tremors and is characterised by slow movement, a shuffling gait, stiff limbs, balance problems and slurred speech.About 10 million people worldwide are living with the condition, the Parkinson's Foundation estimates. It usually appears after age 60, although it sometimes develops before age 50.The exact cause isn't known, but Parkinson's develops when cells that produce one of the brain's chemical messengers — dopamine — begin to deteriorate and die.There is no cure, but there are treatments including medications that affect dopamine levels and a surgically implanted tremor-blocking device. Patients also can benefit from physical and occupational therapy.Simon releasing new album"I began treatment, including taking medication to help with stiffness and other symptoms," Simon said. "There is no tidy or predictable schedule to the illness. It does not consult my calendar before deciding what kind of day I am going to have."Carly Simon says she doesn't want her illness to define her life. (Supplied: Wiki Commons)She also shared that she was treated for basal cell carcinoma, a common form of skin cancer, on her face at the same time. She had surgery, and the cancer was removed, "but the surgery affected my appearance and made me more self-conscious about being seen in public," she said.She said music has been a salve, and on August 14, she will release Comes in Waves, her first album of original songs since 2008."Working on the music gave shape to days that did not always have much shape. It gave me somewhere to go without having to leave the room," she said. "It reminded me that illness can change your life without becoming the whole of your life."AP