Background: Plexiform neurofibroma is a pathognomonic manifestation of Neurofibromatosis type 1 (NF1), a rare autosomal dominant genetic disorder caused by a mutation in chromosome 17q 11.2, affecting approximately 1 in 3000 births. Elephantiasis Neuromatosa (EN) is an uncommon presentation of plexiform neurofibroma, which leads to severe limb hypertrophy and can be mistaken as Filariasis. Here, we present a challenging adult case of EN initially misdiagnosed as filariasis for 15 years. Prompt recognition and accurate diagnosis were crucial for managing rare NF-1 presentations such as EN, addressing treatment complexities, and access challenges. By navigating beyond the traditional borders of diagnosis and treatment, this case sheds light on the intricate management dilemmas faced in such scenarios.

Case Presentation: A 19-year-old Guatemalan male presented with long-standing left lower limb abnormalities, initially suspected as Filariasis. The patient had recently migrated from Guatemala specifically seeking treatment for Filariasis. On physical examination, pronounced enlargement of both the phallus and scrotum was noted, along with palpable cystic masses, prompting clinical suspicion of severe lymphedema secondary to Filariasis. However, further examination revealed extensive masses affecting the thigh, pelvis, genitals, and lower leg, with associated clinical features indicative of NF1. Multiple café-au-lait macules were evident over the chest, back, and torso, with larger lesions around the lower left trunk. Additionally, multiple small nodules consistent with cutaneous neurofibromas were present. MRI showed extensive fluid-filled lesions throughout the pelvis and lower extremities, indicative of plexiform neurofibroma. Biopsy revealed spindle cells positive for S100. Genetic analysis revealed a pathogenic variant within the NF1 gene, confirming the diagnosis of NF1. Treatment with Selumetinib, a selective MEK inhibitor, was considered. However, Trametinib was initiated due to insurance constraints. Remarkably, significant improvement was observed after one month of treatment. Discussion: The case highlights the diagnostic challenges encountered in identifying EN, particularly when it presents as Filariasis. NF-1 diagnostic criteria, including characteristic clinical features and genetic testing, play a vital role in accurate diagnosis. Imaging modalities such as MRI aid in confirming the diagnosis by revealing typical features of plexiform neurofibroma. Treatment options for EN, primarily surgical intervention, pose significant risks due to high risk of bleeding and the potential for recurrence. Although Selumetinib is approved only for pediatric population, Trametinib is a viable alternative as well, demonstrating its efficacy in improving symptoms.