Cotard syndrome
The Cotard delusion, Cotard's syndrome, or Walking Corpse Syndrome is a rare mental disorder in which people hold a delusional belief that they are dead (either figuratively or literally), do not exist, are putrefying, or have lost their blood or internal organs.  In rare instances, it can include delusions of immortality.

# Historical perspective
The syndrome is named after Jules Cotard (18401889), a French neurologist who first described the condition, which he called le delire de negation ("negation delirium"), in a lecture in Paris in 1880. He described the syndrome as having degrees of severity that range from mild to severe. Despair and self-loathing characterize a mild state. Severe state is characterized by intense delusions and chronic depression.
In this lecture, Cotard described a patient with the pseudonym of Mademoiselle X, who denied the existence of God, the Devil, several parts of her body, and her need to eat. Later she believed she was eternally damned and could no longer die a natural death. She later died of starvation.

# Pathophysiology
The underlying psychopathology and neurophysiology of Cotard's Syndrome may be related to other problems involving delusional misidentification. Neurologically, Cotard's is thought to be related to the Capgras delusion, and both are thought to result from a disconnect between the brain areas that recognize faces (fusiform face areas) and the areas that associate emotions with that recognition (the amygdala and other limbic structures). This disconnection creates a sense that the observed face is not the person's it purports to be, and therefore lacks the familiarity that should be associated with it. The disconnect results in a feeling of derealization. If it is the face of a person known to the sufferer, it is experienced as an impostor's (Capgras); if the sufferer sees their own face they may feel no association between it and their sense of self, resulting in a sense that they do not exist.
Literature shows that Cotard's is associated with lesions in the parietal lobe. Patients with Cotard's generally have more brain atrophy than control groups and more median frontal lobe atrophy in particular.
Cotard's syndrome is encountered primarily in psychoses such as schizophrenia. It can arise in the context of neurological or mental illness and is particularly associated with depression and derealization. It has even been described in migraine.
Cotard delusion has also been the result of adverse drug reactions to (val)acyclovir. The symptoms were associated with high serum concentrations of CMMG, the principal metabolite of acyclovir. Patients with impaired renal function seem to be at risk even after dose reduction; in the cited case, haemodialysis cured the delusions in a few hours and it is suggested that this mental state may not always be a cause for psychiatric hospitalization.
Research shows that culture has an impact on the biographical experiences expressed by patients who suffer from Cotard's. This finding supports Bering's view of a cognitive system dedicated to forming illusory representations of immortality. Mainstream thought is that these illusory representations of immortality and other delusions evolved in response to sociological pressures.

# Signs and symptoms
The central symptom in Cotard's syndrome is the delusion of negation. Those who suffer from this illness often deny that they exist or that a certain portion of their body exists. Cotard's syndrome has been found to have three distinct stages. In the first stage - Germination - patients exhibit psychotic depression and hypochondriacal symptoms. The second stage - Blooming - is characterized by the full blown development of the syndrome and the delusions of negation. The third stage - Chronic - is characterized by severe delusions and chronic depression.
People with the Cotard Delusion often become withdrawn from others and they tend to neglect their own hygiene and well-being. The delusion makes it impossible for patients to make sense of reality, which results in an extremely distorted view of the world. This delusion is often found in psychotic patients suffering from schizophrenia. While Cotard's Syndrome doesn't necessitate hallucinations, the strong delusions are comparable to those found in schizophrenic patients.
The novel, "Maitre Mussard's Bequest" ("Das Vermachtnis des Maitre Mussard") by German author Patrick Suskind, describes a strange character, Maitre Mussard, whom we can see, through his own writings, becomes psychosomatically paralyzed (similar to rigor mortis) as a result of a severe case of Cotard delusion.
Distorted Reality
Young and Leafhead describe a modern-day case of Cotard delusion in a patient who suffered brain injury after a motorcycle accident:
 symptoms occurred in the context of more general feelings of unreality and being dead. In January 1990, after his discharge from hospital in Edinburgh, his mother took him to South Africa. He was convinced that he had been taken to hell (which was confirmed by the heat), and that he had died of septicaemia (which had been a risk early in his recovery), or perhaps from AIDS (he had read a story in The Scotsman about someone with AIDS who died from septicaemia), or from an overdose of a yellow fever injection. He thought he had "borrowed my mother's spirit to show me round hell", and that she was asleep in Scotland.
An example of the distorted reality that results from Cotard Syndrome was described in a study of a 14-year-old patient with epilepsy. The child psychiatry OPD he was brought to described his history of expressing themes of death, being sad all the time, decreased play activity, social withdrawal, and disturbed biological function. He would have episodes about twice a year that lasted three weeks to three months at a time. In each episode, the child would say that everyone is dead, including trees. He would also describe himself as being a dead body. He warned that the world would be destroyed within a few hours. He showed no reaction to pleasurable stimuli and showed no interest in any activities.

# Treatment
There are several reports of successful pharmacological treatment. Monotherapeutic and combination strategies are both reported.
Antidepressants, antipsychotics and mood stabilisers are used. Many report positive effect with electroconvulsive therapy, mostly in combination with pharmacotherapy.