Note: I am not stating that the following is true, this is only a theory. Unfortunately I don’t have the scientific vocabulary to describe it perfectly.
The body is deprived of a specific endogenous substance. In PFS, PSSD, PAS and the other syndromes people have reported on this website, this substance would be DHT or testosterone (androgens in general). However the same mechanism causing these syndromes may also be the one causing permanent side effects after taking antipsychotics, by depriving the body of dopamine.
The system which is responsible for creating a response to a substance (receptors and signaling system) may be dependent on the presence of the substance itself. So when an androgen binds to the AR, one of the responses created is to express AR itself, along with the signaling system. When androgens are (almost) completely depleted, receptors and the signaling system will stop being expressed. And this may lead to a complete epigenetic shutdown of receptors and the signaling system. In an attempt to compensate for the silenced signaling system, the body will overexpress AR to an extreme degree. This will paradoxically result in permanent silencing of the androgen signal because overexpressed receptors will not induce any response.
Taking exogenous androgens is the first treatment that comes to mind, however this will not work due to overexpressed AR. In fact it may make the symptoms even worse because the androgen signal will become even weaker. One may reason that exogenous androgens will work by causing downregulation of AR, however this will not occur because exogenous androgens will not induce a stronger androgen signal. Therefore the body will have no reason to downregulate AR.
Many have reported improvement after taking antiandrogenic substances. The improvement is due to either lower androgen levels, which allow the receptors to create a stronger response, or due to downregulation of AR, which will also allow a stronger androgen response. There have been rumours of mice with PSSD induced at a young age being cured by SSRI.
The cure for these syndromes may in fact be a drug which allows you to precisely control the inhibition of the previously depleted substance. So the inhibition must be dose-dependent. This will allow you to inhibit androgens so that the overexpressed receptors can create a response again. If you take it for long enough then the signaling system will hopefully be reactivated. Obviously it is very important to not inhibit androgens too much as otherwise the symptoms may become even worse. And you need to taper off very slowly so that the return of androgens does not overwhelm the body and cause more silencing. I think finasteride is the worst substance to use for this because its 5AR inhibition related to dosage is not linear at all.