A 30-Year-Old Man With a 2-Year History of Rash

Adam R. Taintor, MD

Disclosures

May 18, 2009

Discussion

A Fite's acid-fast bacilli stain (Figure 8) revealed moderately large numbers of acid-fast organisms within nerves and infiltrated histiocytes.

Figure 8.

Fite's acid-fast stain at high power.

Leprosy is an infection caused by Mycobacterium leprae that primarily affects the skin, peripheral nerves, eyes, and mucous membranes. The vast majority of the world's population is immune to the bacillus, including those living in endemic areas.[1] Genetic studies have shown susceptibility loci at 10p13 and 6q25, which are associated with markers shared by the Parkinson's disease genes PARK2 and PACRG.[2,3,4]

The challenge in treating leprosy patients is in categorizing the disease subtype, because different subtypes require different therapeutic regimens. Leprosy is classified according to the Ridley-Jopling classification.[5] Tuberculoid and lepromatous leprosy stand as polar opposites on the clinical spectrum of disease. Along the spectrum between tuberculoid and lepromatous leprosy are borderline-tuberculoid, borderline-borderline, and borderline-lepromatous. According to the WHO classification, tuberculoid and borderline-tuberculoid are considered paucibacillary, while the other subtypes are considered multibacillary.

Based on bilaterally distributed macules, papules, and nodules of various sizes and shapes, our patient was diagnosed with borderline-lepromatous leprosy. He also had widespread asymmetric peripheral nerve involvement.

In leprosy, the individual's cell-mediated immune status correlates with the clinical manifestations of disease.[6] For example, tuberculoid leprosy is characterized by strong cell-mediated immunity. Patients present with localized nerve involvement and few skin lesions. Lepromatous leprosy, on the other hand, has impaired cell-mediated immunity and a strong humoral response with significant antibody production. These patients have extensive nerve involvement and numerous skin lesions with uncontrolled bacterial replication.

Histologically, many acid-fast bacilli, vacuolated giant cells, histiocytes, and nonspecific inflammatory infiltrates with clear subepidermal zoning may be present in lepromatous leprosy.[7] In tuberculoid leprosy, acid-fast bacilli are rare. Tuberculoid granulomas may reach the epidermis without a subepidermal zone of sparing. Granulomas tend to be linear along cutaneous nerves.

Reactional states occur in 25% to 50% of patients of all subtypes except tuberculoid and complicate the treatment of leprosy.[8]

Type 1 reversal reaction is also known as upgrading and is seen only in borderline-borderline patients.[9] It occurs as a result of a delayed-type hypersensitivity reaction with a shift from antibody-mediated to cell-mediated response. The reaction can lead to a lower bacterial load but may result in worsening of neurologic findings and permanent nerve damage.

Erythema nodosum leprosum, also known as type 2 reaction, occurs only in borderline-lepromatous and lepromatous leprosy patients and results from antibody-antigen immune complexes depositing in skin, blood vessel walls, nerves, and other organs.

"Downgrading" occurs only in untreated or noncompliant patients and represents decreasing cell-mediated immunity.[6] Patients present with new lesions, malaise, and fever.

Lucio's reaction, a diffuse nonnodular lepromatous leprosy, is common in Mexico and Central America but rare in other areas.[10] It is associated with thrombotic lesions that are distinguished from erythema nodosum leprosum by an absence of fever, leukocytosis, and tenderness. Acute lesions present as retiform purpura. These lesions frequently progress to chronic ulcers.

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