At the risk of over simplification or being inaccurate – I will attempt, to define a “syndrome” and why it is different than a “disease.” My understanding is that a disease has a known cause.
A syndrome is defined by it’s symptoms – so for Cronkhite-Canada Syndrome, it would include the hundreds of polyps, weight loss, hair loss, loss of appetite, hyperpigmentation, loss of nails, etc. However the cause of those symptoms is not known.
So if you have a disease and somone else has the same disease – you would be having similar reactions to something similar that is going on in your bodies. If you and someone else have the same syndrome you would both have the same symptoms – but the cause of the symptoms would not be known.
I read something that made the most sense to me – it was a progression of the understanding of something that is happening in the body. From least understood to most understood – the progression was; symptom, syndrome, disorder and disease.