Dysautonomia is a rather general term, meaning a condition of dysfunction in the autonomic nervous system... it makes no reference to a specific cause or set of symptoms except that they relate to the "ANS". The autonomic nervous system (ANS) has "central" and "peripheral" components... and can be thought of as controlling the underlying functions of the body, those things beyond direct conscious control... things like heart rate & BP regulation, sweating, digestive processes, etc.
I believe autonomic neuropathy basically means damage/death of the nerves of the autonomic nervous system. Denervation is either same or similar concept... meaning lacking or reduction in population of certain nerves. This would be one possible cause of dysautonomia. It would sometimes be measurable by nerve conduction studies and other things that focus on specific nerve function. It might also be implied by circumstances and a doc could perhaps make the call that it is the most likely underlying cause in some cases where enough information is available.
One classic case is diabetic neuropathy where circumstances of diabetes mellitus can lead to peripheral ANS nerve death... and the ANS is left with bad or missing signals "inputs" and/or unresponsive "outputs"... for example, the "smooth muscles" that constrict veins throughout the body may stop responding.
POTS is one type of dysautonomia. It has a set of criteria that most notably includes the trademark abnormal increase in pulse upon standing (30+ bpm increase). Even so, symptoms go well beyond that. There are many possible "causes", some known some theoretical, and cause can remain unknown.
Additionally, POTS can end up being early signs of a "larger" dysautonomia (like PAF or MSA... pure-autonomic-failure or multiple-system-atrophy) or can be present "along side" a diagnosis of another dysautonomia like NCS (NeuroCardiogenic Syncope). It can also be "secondary" to other disorders that aren't limited strictly to the ANS... but which do tamper with it.
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