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Case Reports
. 2025 Jun 9;17(6):e85630.
doi: 10.7759/cureus.85630. eCollection 2025 Jun.

Amelanotic Nodular Melanoma Over the Knee Region: A Case Report of a Diagnostic Challenge From the United Arab Emirates

Khadiga Abdelmonem  1 , Loay Ghalyoun  2 , Divyashri Ramanathan Nagarajan  2 , Sonia Otsmane  3 , Joaquin Picazo-Yeste  4
Affiliations
Case Reports

Amelanotic Nodular Melanoma Over the Knee Region: A Case Report of a Diagnostic Challenge From the United Arab Emirates

Khadiga Abdelmonem et al. Cureus. .

Abstract

Amelanotic melanoma (AM) is a rare and aggressive subtype of cutaneous melanoma that lacks the characteristic pigmentation, which makes it challenging to diagnose, often resulting in delayed treatment. Nodular melanoma (NM), a subtype of AM, is associated with a poorer prognosis and is infrequently reported in the Middle East and North Africa (MENA) region. AM is a rare and aggressive subtype of cutaneous melanoma, accounting for approximately 1-8% of all melanoma cases. We present the case of a 39-year-old Filipino female with a slowly enlarging, skin-colored lesion on her right patella, initially misdiagnosed as a dermatofibroma. The lesion was later confirmed as type IIIb cutaneous amelanotic nodular melanoma via histopathology and immunohistochemistry, with a Breslow thickness of 5 mm and Clark level IV invasion. Sentinel lymph node biopsy revealed nodal involvement, and the patient underwent wide local excision followed by adjuvant immunotherapy. This report highlights the diagnostic challenges posed by AM, particularly in younger patients and in regions where such cases are rarely reported. Accurate diagnosis requires a high index of suspicion and a multimodal diagnostic approach. Early recognition and intervention are crucial for improving patient outcomes in this aggressive malignancy.

Keywords: knee lesion; misdiagnosis; nodular melanoma; s: amelanotic melanoma; sentinel lymph node; united arab emirates.

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Conflict of interest statement

Human subjects: Consent for treatment and open access publication was obtained or waived by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.

Figures

Figure 1
Figure 1. Right patellar region showing a firm, skin-colored dermal lesion
Figure 2
Figure 2. PET imaging demonstrating no signs of metastasis
PET: positron emission tomography
Figure 3
Figure 3. Scintigraphic image following injection of 2.5 mCi of Tc-99m sulfur colloid demonstrating localization of sentinel lymph node
Figure 4
Figure 4. (A) Histological section demonstrating metastatic melanoma cells within the lymph node. (B) Melanin A stain shows negative expression. (C) S100 positive staining. (D) SOX10 positive staining
See this image and copyright information in PMC

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