Metastatic malignant melanoma arising in a small congenital melanocytic nevus: A case report

Abstract

Congenital Melanocytic Nevi are benign melanocytic proliferations that are present at birth or present shortly afterwards. While giant melanocytic nevi are often associated with a risk of malignancy, the chances of malignant transformation in a small congenital melanocytic nevus are considered to be very low. In under-developed countries like Pakistan, despite melanocytic nevi being very common in the local population, they are not paid any clinical attention or kept under follow-up. However, this case of a young patient with a rapidly metastatic malignant melanoma that involved her spine, liver, lungs and lymph nodes is a very alarming scenario, that urges all dermatologists to be vigilant regarding their examination of congenital melanocytic nevi. It also indicates a gap in the literature pertaining to the prevalence and incidence of malignant melanoma in the local population. We present the case of a 25-year old female patient who had a small congenital melanocytic nevus on the mons pubis, present at birth, and growing proportionately with her age until it reached just over 1cm in size at adulthood. Prior to presentation, the patient had a sudden increase in size of the nevus, change in surface and pigment density, and pain and swelling in the adjacent left inguinal lymph nodes. The patient was also pregnant at the time. Histopathology and Immunohistochemistry confirmed the diagnosis of a cutaneous malignant melanoma. The disease advanced rapidly, and despite local excision with tumor free margins, was found to have systemic metastasis in all major organs within a few weeks of diagnosis, lending the patient a very poor prognosis at a very young age. Congenital Melanocytic Nevi (CMN) are defined as melanocytic nevi that are present at the time of birth or appear shortly thereafter. They may be noted at birth in around 1% of neonates. While large or giant congenital melanocytic nevi are often assumed to carry some risk of malignant transformation, small ones are usually considered inconsequential and are rarely monitored. However, they occur with the largest frequency in the general population and even a small risk of malignancy is significant enough to merit surveillance in these patients. Melanoma is reported infrequently in people of colored skin, particularly in developing countries. But we urge all dermatologists to keep a low threshold of suspicion and follow up any changes such as rapid growth, change in color or ulceration with a prompt histological examination to aid early diagnosis.