The FSH reset hypothesis: optimizing spermatogenesis in azoospermia.
PURPOSE OF REVIEW Elevated follicle-stimulating hormone (FSH) in primary hypogonadism is usually read as maximal but failing testicular stimulation, and affected men are often considered poor candidates for hormonal therapy. This is a hypothesis-generating narrative review rather than an evidence-based treatment recommendation. It re-examines that assumption and asks whether FSH bioactivity, rather than concentration alone, might shape the testicular response. RECENT FINDINGS Circulating FSH is a mixture of glycosylation-dependent isoforms that differ in receptor-binding efficiency in experimental systems. Chronic gonadotropin excess can downregulate and desensitize the FSH receptor in animal and in vitro models. In principle, these mechanisms could combine to produce a state of functional FSH resistance, in which immunoreactive FSH is high while the effective signal in the testes is weaker. FSH suppression-associated rises in inhibin B, contemporary staged conditioning protocols, and stratification of hypergonadotropic men under the APHRODITE criteria are consistent with a strategy of temporary suppression before stimulation. SUMMARY We outline the FSH reset hypothesis, in which a finite period of pituitary suppression reduces inefficient endogenous hormone and may allow receptor recovery before controlled recombinant FSH. We then present a stepwise treatment algorithm as a model for future investigation in selected men with spermatogenic failure. The hypothesis is speculative and remains unproven in prospective trials.