An account of the world's first patient to be diagnosed with Alzheimer's disease has been discovered in a file that had been lost for 90 years.

The patient, a 51-year-old woman from Frankfurt known as Auguste D, was diagnosed by Alois Alzheimer with a form of dementia that subsequently became known as Alzheimer's disease.

Alzheimer described her case in a remarkable lecture delivered to a conference of psychiatrists in Tubingen, southern Germany, on 4 November 1906. The file on her case, including case notes which movingly detail the extent of her mental decline, was described in an article published in 1909 but had not been seen since.

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The discovery of the file was described as a miracle yesterday by Professor Konrad Maurer who came upon it by chance in the archives of the Johann Wolfgang Goethe University psychiatric clinic in Frankfurt. "Holding the missing document with Dr Alzheimer's own handwriting is like holding history in your hand," Professor Maurer said.

The blue cardboard file was well preserved and contained pictures of the patient, samples of her handwriting, a case history, brain tissue analyses and a post-mortem report. The first sign of her illness was a powerful feeling of jealousy towards her husband. She rapidly began to lose her memory and developed delusions and hallucinations. Examination of her brain after death showed the pattern of plaques, neurofibrillary tangles and other changes that have since come to be recognised as the defining characterisitcs of Alzheimer's disease.

The case notes begin on 26 November 1901, recording Dr Alzheimer's interview with his patient. Her answers are given in italics).

"She sits on a bed with a helpless expression. What is your name? Auguste. Last name? Auguste. What is your husband's name? Auguste, I think. Your husband. Ah, my husband. She looks as if she didn't understand the question. Are you married? To Auguste. Mrs D? Yes, yes , Auguste D. How long have you been here? She seems to be trying to remember. Three weeks. What is this? I show her a pencil. A pen.

"At lunch she eats cauliflower and pork. Asked what she is eating she answers spinach. When objects are shown to her she does not remember after a short time which have been shown. In between she always speaks about twins. Asked to write Auguste D she writes Mrs and forgets the rest. It is necessary to repeat every word."

After Auguste D died in 1906, Alzheimer asked for her records and brain to be sent to him in Munich where he was then working. Six months later he delivered his lecture in Tubingen which was published a year later with the title "A characteristic serious disease of the cerebral cortex", but it was not until the eighth edition of the Handbook of Psychiatry in 1910 that the term "Alzheimer's disease" was used.

Professor Maurer, who describes his find in The Lancet, says it lays to rest a dispute among European doctors about whether Auguste D had Alzheimer's disease or another diagnosis such as arteriosclerosis of the brain in which the walls of the blood vessels become progressively thickened cutting off the blood supply.

Notes in the file show that Auguste D had the distinctive signs of a degenerative and not a vascular (blood vessel) dementia and there were no significant signs of arteriosclerosis.

A copy of the file is to go on public display at the house in the village of Marktbreit, near Wurzburg in central Germany, where Alzheimer was born and which was converted to a museum to commemorate his work in 1995.