Neurofibromatosis type 1 — clinical case

Case summary

This four-year-old boy has an established diagnosis of NF1 by the NIH criteria, meeting cafe-au-lait macules and skinfold freckling, and he now presents with a painful, rapidly enlarging, firm lump on his left thigh. The clinical question is whether this represents malignant transformation of a pre-existing plexiform neurofibroma into a malignant peripheral nerve sheath tumour, which is the most feared and life-threatening complication of NF1. [1]

Key clinical issues

The change in the lesion is the red flag. Pain, rapid growth, a change in texture from soft to firm, and a lesion that wakes the child at night are the classic warning features of malignant peripheral nerve sheath tumour within a pre-existing plexiform neurofibroma. This transformation occurs in roughly 8 to 13 per cent of patients with NF1 over a lifetime, and early recognition and complete excision determine survival. The case also prompts review of his overall NF1 surveillance, because a child old enough to have a plexiform neurofibroma also needs vision, blood pressure, developmental and spinal surveillance. [10]

Investigations and management

The urgent investigation is an MRI of the left thigh to define the lesion, a positron-emission tomography scan to assess metabolic activity and detect metastatic disease, and a biopsy to confirm histology. If malignant peripheral nerve sheath tumour is confirmed, management is wide local excision by a sarcoma surgeon followed by oncological assessment for adjuvant therapy. For the broader NF1 care, I would confirm the surveillance plan: annual review of growth, blood pressure, skin, spine and development, annual visual acuity and colour vision until at least age eight, and developmental and educational support. Genetic counselling and cascade testing of first-degree relatives remain central to the long-term plan. [1] [8]

Discussion points

This case tests whether the candidate can integrate the diagnostic criteria, the molecular basis, and the surveillance programme, while recognising a surgical and oncological emergency. The 2021 revised criteria confirm the NF1 diagnosis, the neurofibromin/RAS mechanism explains why MEK inhibition can treat plexiform disease, and the warning features of malignant transformation must trigger urgent imaging and biopsy. The candidate who frames the whole discussion around the family, with cascade testing and reproductive counselling, demonstrates the fellowship standard. [5]