Abstract
BACKGROUND: Isolated congenital anosmia (ICA) traditionally represents an irreversible sensory disorder affecting 1 in 5,000-10,000 individuals. This case demonstrates rare partial olfactory recovery in childhood-onset anosmia following corticosteroid therapy, providing novel insights into olfactory neuroplasticity and therapeutic potential. CASE PRESENTATION: A 32-year-old woman with lifelong anosmia, diagnosed with ICA at age 20 using Sniffin' Sticks testing (2013), experienced first olfactory perceptions in 2014 following one week of oral corticosteroids and nine months of topical mometasone. MRI (2021) revealed barely visible olfactory bulbs, narrow olfactory clefts, minor ethmoid sinus inflammation, but normal-depth olfactory sulci and typical skull base morphology. Recent psychophysical testing (2025) demonstrated orthonasal hyposmia (TDI score 24) and retronasal hyposmia (11/20). Electrophysiological assessment detected preserved olfactory event-related potentials to hydrogen sulfide and phenyl ethyl alcohol, confirming functional neural circuitry. Recovery was complicated by parosmia, with foods like garlic, eggs and meat perceived as intensely unpleasant and faecal-smelling, leading to dietary modifications and preference for low-odour foods. Patient reported childhood social difficulties related to anosmia, with ongoing evolution of olfactory function over the past decade. Current treatment includes tapered systemic and topical corticosteroids, intranasal vitamin A drops (10,000 IU/day) and olfactory training, with recent improvements including tolerance of previously aversive foods. CONCLUSIONS: This case challenges the irreversibility paradigm of childhood-onset anosmia and demonstrates that olfactory recovery is possible even after decades, potentially mediated by anti-inflammatory effects and neurogenic plasticity. The emergence of parosmia during recovery reflects maladaptive neuroplasticity during olfactory regeneration. Combined corticosteroid therapy, vitamin A supplementation and olfactory training may offer therapeutic hope for similar patients, warranting further investigation of inflammatory modulation and neuroregenerative approaches in congenital olfactory disorders.