Segmental congenital solitary plaque on the shoulder: A rare presentation of neurofibromatosis type 1

INTRODUCTION

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder characterized by the development of neurofibromas, café-au-lait macules, Lisch nodules, and other manifestations. Plexiform neurofibromas, a subtype of neurofibroma, are often associated with NF1 and can present as congenital, slow-growing lesions. However, isolated segmental plexiform neurofibromas without other obvious clinical features of NF1 pose a diagnostic challenge. This report presents a case of a solitary segmental plexiform neurofibroma in a middle-aged woman, highlighting the importance of detailed histopathological and ophthalmological evaluations in such instances.

CASE REPORT

A 50-year-old female presented with a congenital, asymptomatic hyperpigmented plaque on the right shoulder, involving both anterior and posterior aspects [Figure 1]. The plaque measured approximately 10 cm long and 8 cm wide. The lesion had been present since birth, along with a pedunculated growth on the back of the neck. It grew proportionately and remained stable after childhood, with no reported episodes of ulceration, oozing, or rapid growth. Physical examination revealed a soft-to-firm plaque with overlying skin appearing loose and pendulous on the back of the neck [Figure 2]. No other pigmented lesions or neurofibromas were observed elsewhere on the body. The patient reported no family history of similar lesions. Dermoscopy showed increased skin markings with a yellowish tinge.

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Figure 1:

Segmental hyperpigmented plaque with irregular surface.

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Figure 2:

Pendulous growth on the posterior aspect of the plaque.

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A biopsy was performed to establish a definitive diagnosis. Histopathological examination revealed an ill-circumscribed dermal spindle cell neoplasm with multiple nerve fascicles [Figure 3]. The spindle cells exhibited elongated, pointed, and wavy nuclei, with some showing an “S” shape [Figure 4]. Mast cells were also present within the neoplasm. These findings were consistent with a plexiform neurofibroma.

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Figure 3:

Nerve bundles within the spindle cell neoplasm (Hematoxylin and eosin, 40x).

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Figure 4:

Spindle cells with characteristic wavy nuclei (Hemtoxylin and eosin, 40x).

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DISCUSSION

This case underscores the importance of considering plexiform neurofibroma in the differential diagnosis of congenital hyperpigmented plaques, even in the absence of other clinical features of NF1. The patient was referred for an ophthalmological examination, which revealed Lisch nodules in both eyes, identified through slit-lamp examination. These nodules were not detectable with torchlight examination. The patient exhibited no other features of NF1.

NF is a phakomatosis inherited in an autosomal dominant pattern, caused by a mutation in the neurofibromin gene. It is characterized by the development of neurofibromas, café-aulait macules, iris hamartomas (Lisch nodules), optic gliomas, bone deformities, and freckling. The diagnosis is based on the criteria established by the National Institutes of Health in 1987^[1], have since been revised. The criteria include:

1. More than six café-au-lait macules (≥5 mm in diameter in prepubertal individuals, ≥15 mm in diameter in post-pubertal individuals).

2. Axillary or inguinal freckling.

3. Presence of two or more neurofibromas (cutaneous or subcutaneous).

4. Lisch nodules (iris hamartomas).

5. Optic pathway gliomas.

6. A family history of NF1 (a parent with NF1).

A diagnosis of NF1 requires at least two of these criteria. The 2021 modification^[2] has included genetic testing as one of the diagnostic criteria to facilitate early diagnosis.

Plexiform neurofibromas are typically present from birth and are strongly associated with NF1. They usually develop along nerves and cause soft tissue overgrowth. They are slow-growing and mostly painless. On palpation, the lesions have a “bag of worms” feel. Histopathologically, these tumors consist of a mixture of spindle-shaped Schwann cells, fibroblasts, mast cells, and other cellular elements. They can involve multiple layers of tissue, including the skin, subcutaneous tissue, muscles, and nerves. Initially, there are multiple nerve fascicles in the tumor, and later, the cells might spill out and become diffuse.^[3]

There are reports of plexiform neurofibromas occurring in the head and neck area without associated NF1.^[4] However, NF1 occurring as a single plexiform neurofibroma without other cutaneous neurofibromas, café-au-lait macules is a rare presentation.

Plexiform neurofibromas can cause overgrowth of affected tissues, leading to cosmetic concerns, functional impairment, and the potential for complications such as malignant peripheral nerve sheath tumors (MPNSTs). MPNSTs are aggressive tumors that can metastasize, making early detection and management critical.^[5]

Treatment of plexiform neurofibromas typically involves surgical excision for symptomatic lesions. Debulking surgery may be performed to reduce the size and improve function or appearance, especially when complete excision is not feasible. In some cases, targeted therapies may be considered for inoperable or recurrent lesions. However, surgical resection can be complicated by the size, location, and involvement of surrounding structures, making complete excision challenging. Newer medical management options, including the mitogen-activated protein kinase kinase (MEK) inhibitor selumetinib and the tyrosine kinase inhibitor cabozantinib, show promising results.^[6]

It is essential to accurately characterize isolated lesions, as in this case, where other features of type 1 neurofibromatosis were lacking and the biopsy prompted further evaluation and a detailed eye examination. These patients require lifelong follow-up due to the risk of complications. Regular monitoring is crucial for detecting malignant transformation, neurological deficits, or other associated conditions, thereby improving long-term outcomes.

CONCLUSION

This case highlights the diagnostic complexity presented by plexiform neurofibromas when they manifest without the typical constellation of NF1 features.