If symptoms persisted after a few weeks at a local Casualty Clearing Station, which would normally be close enough to the front line to hear artillery fire, a casualty might be evacuated to one of four dedicated psychiatric centres which had been set up further behind the lines, and were labelled as "NYDN – Not Yet Diagnosed Nervous" pending further investigation by medical specialists. Although the Battle of Passchendaele generally became a byword for horror, the number of cases of shell shock were relatively few. 5,346 shell shock cases reached the Casualty Clearing Station, or roughly 1% of the British forces engaged. 3,963 (or just under 75%) of these men returned to active service without being referred to a hospital for specialist treatment. The number of shell shock cases reduced throughout the battle, and the epidemic of illness was ended.During 1917, "shell shock" was entirely banned as a diagnosis in the British Army, and mentions of it were censored, even in medical journals. Chronic treatment
The treatment of chronic shell shock varied widely according to the details of the symptoms, the views of the doctors involved, and other factors including the rank and class of the patient. There were so many officers and men with shell shock that 19 British military hospitals were wholly devoted to the treatment of cases. Ten years after the war, 65,000 veterans of the war were still receiving treatment for it in Britain. In France it was possible to visit aged shell shock victims in hospital in 1960.
Physical causes
2015 research by Johns Hopkins University has found that the brain tissue of combat veterans who have been exposed to improvised explosive devices (IEDs) exhibit a pattern of injury in the areas responsible for decision making, memory and reasoning. This evidence has led the researchers to conclude that shell shock may not only be a psychological disorder, since the symptoms exhibited by affected individuals from the First World War are very similar to these injuries. Immense pressure changes are involved in shell shock. Even mild changes in air pressure from weather have been linked to changes in behavior.There is also evidence to suggest that the type of warfare faced by soldiers would affect the probability of shell shock symptoms developing. First-hand reports from medical doctors at the time note that rates of such conditions decreased once the war was mobilized again during the 1918 German offensive, following the 1916–1917 period where the highest rates of shell shock can be found. This could suggest that it was trench warfare, and the experience of siege warfare specifically, that led to the development of these symptoms. Cowardice
Some men with shell shock were put on trial, and even executed, for military crimes including desertion and cowardice. While it was recognised that the stresses of war could cause men to break down, a lasting episode was likely to be seen as symptomatic of an underlying lack of character.