Do you always have a preceding episode of diarrhoea in Guillain-Barré syndrome?

Edit: I've reworked this post a little. It was done late at night, and was, like me at the time, confused! ;)

Guillain-Barré syndrome consists of four subtypes of acute peripheral neuropathies. It most commonly presents as a peripheral motor and sensory neuropathy, but can spread to involve more critical muscles, like those for respiration.

Guillain-Barré is believed to be predominantly an auto-immune disorder. Both antibody and cell-mediated reactions to peripheral nerve myelin are involved. As the condition progresses, segmental demyelination results. Eventually, if the process is ongoing and severe, there is axonal damage and nerve cell death; at this point, regeneration cannot occur.

Why does the body start attacking peripheral nerve myelin? It is believed to be a case of mistaken identity - certain antigens that the body is exposed to are sufficiently similar to antigens on the peripheral myelin to incite an attack by the immune system in susceptible patients. But what is this cross-reactive antigen?

It is clear that, at least in many cases, the responsible agent is infectious. In particular, Campalobacter jejuni, Mycoplasma and viral infections (e.g. varicella-zoster, mumps, cytomegalovirus) have been implicated, although the long list includes immunisations, antitoxins, surgery, trauma and malignancy.

So, no, you don't always have a preceding episode of diarrhoea. If you are already suspicious that you are dealing with Guillian-Barré and this does come up in the history, it does contribute somewhat to the likelihood that you are right in your suspicions.