Friederich Nietzsche and the seduction of Occam's razor.

Friedrich Nietzsche developed dementia at the age of 44 years. It is generally assumed that the cause of his dementia was neurosyphilis or general pareisis of the insane (GPI). Others have proposed frontal-based meningioma as the underlying cause. We have reviewed Nietzsche's medical history and evaluated the evidence from the medical examinations he underwent by various physicians. We have viewed the possible diagnosis of GPI or meningioma in light of present neuro-ophthalmic understanding and found that Nietzsche did not have the neurological or neuro-ophthalmic symptoms consistent with a diagnosis of GPI. The anisocoria which was assumed to be Argyll Robertson pupil was present since he was six years of age. He did not have tongue tremor, lacked progressive motor features and lived at least 12 years following the onset of his neurological signs. Furthermore, the headaches that have been attributed to a frontal-based tumour were present since childhood and the pupil abnormality that has been interpreted as an "afferent pupillary defect" had the characteristics of an abnormality of the efferent pupillary innervation. None of the medical records or photographs suggest there was any ocular misalignment. We concluded that neither diagnosis of GPI nor frontal-based meningioma is convincing. It is likely that Nietzsche suffered from migraines, his blindness in his right eye was a consequence of high progressive myopia associated with retinal degeneration, his anisocoria explained by unilateral tonic pupil, and his dementia by an underlying psychiatric disease.