| Well....getting back to the original question, pseudobulbs are a bit like a storage facility for moisture and nutrients. When they are full, they're plump. If the plant has had to draw upon those reserves the bulbs first become wrinkled then more and more shriveled as the stores are depleted.
The plant has to turn to its reserves usually for one reason, that being that is is not able to take in what it needs form its environment. There are only 2 reasons why a plant might not be getting what it needs form its environment: 1) what is needs is not available - for example a dendrobium in the wild needs to draw on its reserves during the dry season or a plant in your collection needs to draw upon its reserves if its not being watered frequently enough, or 2) the mechanism by which it takes in moisture and nutrients is compromised - for example an orchid that has lost its roots to damage or rot is not able to take in water and nutrients even if they are present in the environment.
Some orchids have naturally wrinkly, pleated, or ribbed pseudobulbs so it is necessary to know the characteristics of the orchid being grown in order to correctly interpret the condition of the pseudobulbs.
Finally, old pseudobulbs will "deflate" and die off naturally once it is of no more use to the plant. This happened recently to the oldest back bulb on my only lycaste. It quickly turned brown and dried up/became hollow.
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