What Is the Lepromin Skin Test?

    A lepromin skin test is used to determine the type of leprosy a patient has contracted. The lepromin skin test is also called the leprosy skin test.

    Leprosy is a chronic condition caused by the bacteria Mycobacterium leprae (M. leprae). The disease is commonly found in Asia and Africa and is transmitted through mucus from the nose, eyes, and mouth of an infected person. The disease has a long incubation time; symptoms can take up to 20 years to appear.

    Leprosy affects the skin, nerves, eyes, and upper respiratory tract. In men, the disease can affect the testes.

    Leprosy used to be a significant public health concern worldwide. However, the World Health Organization (WHO) reports that, with multidrug therapy, the prevalence of the disease has been reduced by 90 percent. It fell from 21.1 cases per 10,000 inhabitants in 1991 to less than 1 case per 10, 000 inhabitants in 2000 (WHO).

    Luckily, the disease can be effectively treated—and even cured—if it is caught in the early stages. Once leprosy has been diagnosed, your doctor must determine which type of leprosy you have in order to develop a treatment plan.

    Why Is the Test Ordered?

    A skin biopsy is commonly used to diagnose leprosy. A skin biopsy involves removing a small section of skin for laboratory testing. In patients with symptoms of leprosy, a lepromin skin test may be ordered in conjunction with the biopsy to simultaneously confirm the presence and type of leprosy.

    Symptoms of leprosy include:

    • skin lesions that do not heal for several weeks or months
    • skin lesions that are lighter in color or are less sensitive to heat, pain, or touch than unaffected skin
    • skin thickening or scarring
    • nerve damage leading to numbness or lack of sensation in the extremities
    • weakening of the muscles, which gets worse over time

    There are several types of leprosy, ranging from mild (indeterminate) to severe (lepromatous). Depending on the clinical features of the disease, leprosy may be classified as:

    • indeterminate leprosy (IL)
    • tuberculoid leprosy (TL)
    • borderline tuberculoid leprosy (BT)
    • borderline borderline leprosy (BB)
    • borderline lepromatous leprosy (BL)
    • lepromatous leprosy (LL)

    Your doctor must determine which type of leprosy you have in order to provide the correct treatment.

    How is the test Performed?

    A lepromin skin test is performed by injecting a small sample of inactivated M. leprae under your skin. The term “inactivated” means that the bacterium is not able to cause infection. The bacterium is usually injected into the forearm. A small lump will form at the injection site, indicating that the correct amount of bacterium has been injected at the correct depth in the skin for the test to be effective.

    You will need to be examined three days after the injection to see if you have had a reaction to the bacterium. If no reaction occurs, you will need to be examined again in 28 days. Specific reactions at the injection site indicate certain types of leprosy.

    Preparing for the Test

    No preparation is necessary before this test. If you have skin irritation or a skin disorder such as dermatitis, the injection should be made on a part of your skin that is not affected. Skin redness or irritation due to an unrelated skin disorder may produce a false positive result on the lepromin skin test. Performing the test on an unaffected area will help to ensure that the test is accurate.

    What Are the Risks of the Test?

    Risks associated with a lepromin skin test are minor. The injection may cause a slight burning or stinging sensation. The injection site may also be itchy after the injection.

    In very rare cases, an allergic reaction may occur following the injection. An allergic reaction may result in:

    • shortness of breath
    • itching
    • hives (rarely)

    If these symptoms occur, seek help from your doctor to ensure that the reaction is not serious.

    Interpreting the Test Results

    The results of the lepromin skin test are based on changes in the skin that occur at the injection site. Redness, swelling, or other skin changes indicate the presence of tuberculoid and borderline tuberculoid leprosy. Patients that have tested positive for leprosy during a biopsy but do not have a skin reaction typically have lepromatous leprosy.

    If your biopsy and skin test indicate that you have any form of leprosy, your doctor will most likely prescribe the antibiotics dapsone, rifampicin, and clofazimine, which you may have to take for months or even years to treat the disease.