Reaksi Kusta

01Pathophysiology

ENL is fundamentally a Type III hypersensitivity reaction (Arthus-type), and understanding this mechanism is the key to answering questions about it correctly.

In lepromatous and borderline lepromatous leprosy, the patient has a defective cell-mediated immune response against M. leprae, which allows the organism to proliferate unchecked to very high numbers. This produces a large pool of circulating mycobacterial antigens. When these antigens combine with host antibodies (primarily IgG and IgM), they form circulating immune complexes. These complexes deposit in small blood vessels and tissues throughout the body, including the skin, peripheral nerves, eyes, joints, lymph nodes, kidneys, and testes.

Once deposited, the immune complexes activate the complement cascade (particularly C3a and C5a), generating chemotactic signals that recruit neutrophils to the site. Neutrophil degranulation releases proteolytic enzymes and reactive oxygen species, causing direct tissue injury. Simultaneously, there is a surge in tumor necrosis factor-alpha (TNF-alpha) and other pro-inflammatory cytokines (IL-6, IL-8), which accounts for the systemic symptoms of fever, malaise, and the acute inflammatory character of the skin lesions.

This pathophysiology directly explains the clinical picture: the tender erythematous nodules represent neutrophil-rich inflammation around immune complex deposits in the dermis and subcutis. The vasculitis component explains why lesions can vesiculate, become hemorrhagic, or even ulcerate. The systemic deposition of complexes in distant organs explains why ENL is not merely a skin disease but a multisystem inflammatory syndrome. Glomerulonephritis results from renal immune complex deposition, orchitis from testicular involvement, and iridocyclitis from ocular deposition.

A critical concept to remember: ENL can occur before, during, or after completion of MDT. It is not a sign of treatment failure. Rather, the killing of bacilli by MDT releases large quantities of antigen, which paradoxically fuels more immune complex formation. This is why MDT must never be stopped during a reaction.

02Classification and Clinical Manifestation

Lepra Reactions: Type Comparison

ENL Severity Classification

Organ-System Involvement

03Diagnostic Workup

Summary Table

The diagnosis of ENL is primarily clinical. A patient with established lepromatous or borderline lepromatous leprosy who develops new crops of tender red nodules with systemic features (fever, joint pain, nerve pain) has ENL until proven otherwise. The clinical context is your most important diagnostic tool.

The slit-skin smear should already be part of the patient's leprosy workup. In ENL patients, the bacterial index is characteristically high (BI 4+ to 6+), confirming multibacillary disease. This test does not diagnose the reaction itself but confirms the type of leprosy that makes ENL possible.

Skin biopsy is the gold standard when the diagnosis is uncertain or when you need to distinguish ENL from a Type 1 reversal reaction. The hallmark finding is dense neutrophilic infiltration of the dermis and subcutaneous tissue, often accompanied by small-vessel vasculitis and evidence of immune complex deposition. This contrasts sharply with the granulomatous, lymphocyte-rich pattern of a Type 1 reaction. Immunofluorescence may show granular deposits of immunoglobulin and complement along vessel walls, confirming immune complex-mediated injury.

Laboratory studies are supportive, not diagnostic. Elevated ESR and CRP reflect systemic inflammation. A complete blood count typically shows leukocytosis with neutrophilia. In patients with severe or recurrent ENL, check urinalysis for proteinuria and hematuria to screen for glomerulonephritis, and perform a slit-lamp examination if ocular symptoms are present.

04Management and Treatment

Step 1: Do not stop MDT. This is the single most tested principle. A vignette may describe a patient developing ENL while on treatment, and one of the answer choices will be "discontinue MDT." This is always wrong. MDT treats the underlying infection and must continue throughout the reaction.

Step 2: Assess severity. The next best step depends on whether the reaction is mild, moderate, or severe. For mild ENL with only a few nodules and no systemic symptoms, NSAIDs and rest are sufficient. Most mild episodes resolve within a few days.

Step 3: Initiate corticosteroids for moderate to severe ENL. Prednisolone is the first-line anti-inflammatory agent. Start at 40 to 60 mg/day as a single morning dose. The total duration of the taper should be at least 12 weeks according to WHO guidelines. A common tapering schedule reduces the dose by 5 to 10 mg every 2 weeks. Rapid tapers lead to rebound reactions, which is a frequently tested pitfall. Patients on prolonged steroids need monitoring for hyperglycemia, osteoporosis, and opportunistic infections.

Step 4: Thalidomide for severe or chronic recurrent ENL. Thalidomide is the drug of choice for severe and recurrent ENL because it directly inhibits TNF-alpha production, the central cytokine driving ENL inflammation. The initial dose is 300 to 400 mg/day, given at bedtime due to sedative effects. Once symptoms are controlled (usually within 48 to 72 hours), taper gradually to a maintenance dose of 50 to 100 mg/day. Response to thalidomide is often dramatic and rapid, which itself is a diagnostic clue in ambiguous cases.

The critical contraindication: thalidomide is an absolute teratogen (FDA Category X). It causes phocomelia (limb reduction defects) and other severe birth defects. In women of reproductive age, it must never be prescribed unless pregnancy is completely excluded and two forms of contraception are in place. In many clinical settings, especially where pregnancy testing is unreliable, thalidomide is simply avoided in this population.

Step 5: Alternatives when thalidomide is contraindicated. For women of childbearing potential with severe or recurrent ENL, increase clofazimine to 300 mg/day (the maximum recommended dose). Clofazimine has intrinsic anti-inflammatory properties through inhibition of neutrophil motility and complement activation. However, it takes 4 to 6 weeks to achieve its anti-inflammatory effect, so it must be used alongside corticosteroids during the acute phase. The maximum duration at 300 mg/day is 12 months, after which it should be reduced to 100 mg/day to minimize skin discoloration (reddish-brown pigmentation). Pentoxifylline (400 mg three times daily) is another adjunctive option that inhibits TNF-alpha, though evidence is less robust than for thalidomide.

Step 6: Manage organ-threatening complications. Any evidence of neuritis warrants prednisolone regardless of overall ENL severity, because nerve damage can become irreversible within hours to days. Iridocyclitis requires topical steroids and atropine drops to prevent synechiae. Orchitis may require scrotal support and analgesics in addition to systemic steroids.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common mistake students make with ENL is confusing it with a Type 1 reversal reaction. Both are lepra reactions. Both can cause neuritis. Both are tested frequently. But they differ in every way that matters for the exam: the immune mechanism (Type III vs. Type IV), the leprosy subtype (LL/BL vs. borderline spectrum), the skin findings (new nodules vs. inflamed old lesions), the biopsy (neutrophils vs. granulomas), and the treatment of choice for refractory cases (thalidomide vs. corticosteroids alone). When a vignette describes a leprosy patient with "new crops of tender red nodules" and fever, the answer is ENL. When it describes "swelling and reddening of pre-existing hypopigmented patches," the answer is a reversal reaction.

The second trap involves stopping MDT during a reaction. This is a classic distractor answer. Students reason that since MDT may precipitate the reaction, stopping it should help. It does not. MDT must continue, and examiners specifically test whether you know this.

The third trap centers on thalidomide and pregnancy. A vignette may describe a young woman with severe recurrent ENL who has failed corticosteroids. The temptation is to choose thalidomide because it is the most effective drug. But if the patient is of reproductive age without confirmed contraception, thalidomide is absolutely wrong. The correct answer in this scenario is high-dose clofazimine with continued corticosteroids, or pentoxifylline as an adjunct.

Finally, remember that ENL is a multisystem disease, not just a skin condition. A question may focus on orchitis, glomerulonephritis, or iridocyclitis in a leprosy patient without emphasizing the skin nodules. Recognizing that these organ manifestations are part of ENL (immune complex deposition in multiple tissues) is the core competency being tested.