How Acral Lentiginous Melanoma Is Diagnosed

Diagnosis of acral lentiginous melanoma (ALM) typically involves a biopsy (removing a sample tissue for examination in a lab). ALM can look similar to other types of skin cancer, so evaluation by a dermatopathologist (a doctor who specializes in diagnosing diseases by looking at samples of skin, hair, and nails) is required to make an accurate diagnosis.

The word "acral" is derived from the Greek word referring to the highest or topmost portion of the limbs. The word "lentiginous" refers to the initial origin of these tumors as a macular (flat) brown spot resembling a benign lentigo or liver spot.

ALM is highly curable when caught early, underscoring the importance of early diagnosis and treatment.

This article will review ALM diagnosis.

Self-Checks

The earliest sign of acral lentiginous melanoma (ALM) is an oddly shaped and discolored patch of skin surrounded by normal skin. The skin may be raised, with black, gray, tan, red, or brown discoloration, and have irregular borders. Sometimes a brown or tan streak may appear under the nail of your hands or feet, especially the big toe or thumb.

ALM is incredibly rare, but if you see one or more of the following skin changes, seek immediate medical attention:

• Ulceration or bleeding at the sight of a new oddly shaped or discolored patch of skin
• A discolored skin patch that has grown 
• Irregular area of skin greater than 6 millimeters
• A skin patch that has developed irregular borders
  

Physical Examination 

After sharing your signs and symptoms, a healthcare professional will perform a physical exam, looking at all the skin of the body. A full-body skin exam is done if you have:

• Suspicious moles or skin lesions
• Symptoms of early skin cancer
• A history of previous skin cancer
• 50 or more moles
• Atypical moles, also known as dysplastic nevi
• A family history of skin cancer.

During the exam, healthcare providers will look for suspicious growths, moles, or lesions on the skin, including by parting your hair to check the scalp. They will often use a bright light and sometimes a magnifying lens for a more thorough examination. 

Along with identifying ominous characteristics of your mole using the ABCDE rule, your healthcare provider may also point out other signs of melanoma, including:

• Elevation, such as thickening or raising of a previously flat mole
• Scaling, erosion, oozing, bleeding, or crusting at the skin’s surface
• Redness, swelling, or small new patches of color around a larger lesion, called satellite pigmentations, of the surrounding skin
• Itching, tingling, or burning sensation on light touch
• Friability of the skin, such as softening or small pieces that break off easily

In the early stages, it can be hard to tell the difference between ALM and benign nevi (noncancerous moles), so your healthcare provider or dermatologist may use dermoscopy.

This is a special procedure that can help get an accurate diagnosis. In dermoscopy, your healthcare provider will use a microscope and incandescent light to examine the detail of minute structures of the melanocytic skin lesions. Dermoscopy uncovers hard-to-see skin changes that are not visible by the naked eye.

Biopsy

If ALM is suspected, your healthcare provider will recommend a biopsy, a procedure in which a sample of tissue is removed and sent to a lab to be studied under a microscope.

A narrow margin excisional biopsy is recommended for the diagnosis of ALM. During this procedure, the entire tumor and a small amount of normal tissue around it (depending on the thickness of the tumor) are surgically removed. The tissue is then examined by a dermatopathologist under a microscope for signs of malignancy and staging.

Labs and Imaging 

If you have local ALM without spread and are otherwise asymptomatic, imaging studies and other laboratory tests such as blood work are not recommended.

In later stages of the disease, your healthcare provider may order a blood test to measure levels of the enzyme lactate dehydrogenase (LDH). Elevated LDH levels can indicate tissue damage and help determine if the cancer has metastasized (spread).

A chest X-ray may also be used to detect metastasis to the lungs. However, imaging techniques tend to have a high rate of false positives (results show you have the condition when, in fact, you do not) for cutaneous melanomas such as ALM.

Differential Diagnosis

The differential diagnosis—process of differentiating between two or more conditions—for ALM is relatively broad. The list of other conditions that can mimic ALM include:

• Other melanocytic neoplasms (tumors on the skin) such as lentigo, congenital acral nevi, and acquired acral nevi
• Fungal and bacterial infections
• Trauma-related hemorrhage (talon noir)
• Terra firma-forme dermatosis (black or brown raised areas of skin)
• Chronic wounds
• Verrucae (warts)
• Other skin cancers that may have secondary pigmentation (pigment transferred by another cell) such as squamous cell carcinoma or porocarcinoma, or cutaneous melanomas

Summary 

A biopsy of the ALM lesion in question is needed to make a diagnosis. Prior to a biopsy, a healthcare provider will ask you about your signs and symptoms and examine the affected area. 

A Word From Verywell

ALM is incredibly rare, so it's likely that your skin changes are the result of another condition. Still, knowing the signs and symptoms of ALM can lead to early diagnosis and treatment. This is key, given that ALM is a highly curable condition when addressed early.