Acral lentiginous melanoma (ALM) is a special presentation of cutaneous melanoma arising on the sole, palm, fingernail or toenail bed. ALM occurs most often in Asians, sub-Saharan Africans, and African Americans, comprising 50 to 70% of the melanomas of the skin found in these populations. It occurs most often in older males (60 years) and often grows slowly over a period of years. The delay in development of the tumor is the reason these tumors are often discovered only when nodules appear or in case of nail involvement, the nail is shed; therefore, the prognosis is poor. The tumor may be misdiagnosed as a verruca plantaris, subungual hematoma, or an onychomycosis of the fingernail or the nail of the large toe. Subungual melanoma most often occurs on the nail bed of the thumb or large toe. The clinical features are less striking than in other melanomas, appearing in the radial growth phase as macules: dark brown, blue-black, or black, with little variegation and often ill-defined.
Causes of Acral Lentiginous Melanoma
Relatively rare compared to SSM in whites. Probably same incidence in Asians/blacks who have fewer melanomas in general. The pigmented macules that are frequently seen on the soles of African blacks could be comparable with Clark’s dysplastic melanocytic nevi.
Symptoms of Acral Lentiginous Melanoma
- asymmetry of lesion
- border irregularity
- bleeding
- crusting
- color change or variegation
- longitudinal tan, black, or brown streak on a finger or toe nail
- pigmentation of proximal nail fold
- areas of dark pigmentation on palms of hands or soles of feet
Diagnosis
In the medical literature, melanoma diagnosis is often divided into clinical diagnosis and pathological diagnosis. Clinical diagnosis includes first recognizing the clinical appearance is abnormal (by either a patient or doctor), recommending appropriate removal of tumor, and possible radiological testing (chest x-rays, CT scan, PET scan) and bloodwork (CBC, LDH,). Pathological diagnosis comes after the removed lesion is examined in the lab under a microscope. This exam includes histological criteria results that will enable the treating physician to both stage and decide on future treatments for the patient. Usually, the clinical and pathological diagnoses are similar, but in cases of thin melanomas that are invasive or ulcerated, the pathological diagnosis will be more reflective of the true situation.
Treatment
In considering surgical excision, it is important that the extent of the lesion be ascertained by viewing the lesion with a Wood’s lamp and epiluminescence microscopy. The borders of the tumor are indistinct or blurred. There may be a spread of pigment around the nail and onto the nail fold. Subungual ALM and volar type ALM: amputation [toe(s), finger(s)] and volar and plantar ALM wide excision with split skin grafting. Sentinel lymph node procedure necessary in most cases.
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