eMedicine Specialties > Dermatology > Mycobacterial Infections

Papulonecrotic Tuberculids

Author: Robert L Chen, MD, PhD, Instructor, Department of Medicine, Section of Dermatology, University of Chicago Medical Center
Coauthor(s): David Barnette, Jr, MD, Chief of Dermatopathology, Departments of Internal Medicine and Dermatology, Naval Medical Center at San Diego
Contributor Information and Disclosures

Updated: Jan 26, 2007

Introduction

Background

The tuberculids, first described by Darier in 1896, represent a form of cutaneous hypersensitivity reaction to tuberculosis (TB) antigens. Although many types of tuberculids have been described, most are now understood to not be uniquely caused by TB. However, papulonecrotic tuberculids (PNTs) and lichen scrofulosorum are still widely accepted as true tuberculids.

The entity PNT was first established by Pautrier in 1936 as a distinct TB-associated disorder, when he described the characteristic clinical and histopathologic features. PNT is a chronic, recurrent, and symmetric eruption of necrotizing skin papules arising in crops, involving primarily the arms and the legs. A hallmark of this condition is that lesions heal with varioliform scarring. The eruption is believed to represent a hypersensitivity reaction to TB antigens released from a distant focus of infection. Most patients react markedly to the Mantoux skin test (purified protein derivative, PPD) and may exhibit other evidence of current or past TB infection.

Pathophysiology

The pathophysiology of PNT is controversial. Most authors believe this disease entity is triggered by an initial Arthus reaction to mycobacterial antigens. This is then followed by a hypersensitivity reaction in which antigens undergo opsonization by antibodies, followed by immune complex deposition in small cutaneous blood vessels. The ensuing complement cascade triggers a leukocytoclastic vasculitis, leading to destruction of vessel walls with ensuing tissue necrosis. However, other authors dispute this mechanism, citing the lack of leukocytoclastic vasculitis in some cases. Instead, they propose that the primary lesion is the result of subacute lymphohistiocytic vasculitis that leads to thrombosis and subsequent tissue necrosis.

Whatever underlies the pathophysiology, a consensus has been reached that PNT represents a true hypersensitivity reaction rather than the result of a local cutaneous TB infection. This is based on the observation that PNT lesions have consistently failed to either stain positive for, or culture out, mycobacterial organisms. Although the organisms are absent, mycobacterial DNA have been detected in approximately half of the biopsy specimens subjected to polymerase chain reaction. These observations support the idea that lesions of PNT are the result of released mycobacterial antigens in the setting of a concurrent but distant infection.

Frequency

United States

A decreasing incidence of PNT began in the second half of the 1900s and the decline continues to this day. This phenomenon is attributed to aggressive TB control now found in wide practice. Currently, almost all cases come from areas outside of North America with high endemic rates of TB. However, a rare US case, involving a previously healthy 9-year-old girl from Chicago, Ill, was reported in 1990. Historically, reports indicate that young women and children are especially susceptible to this disorder. PNT-like lesions have also been associated with other mycobacterial infections, including Mycobacterium bovis and Mycobacterium kansasii, and from BCG vaccination. With the increased incidence of TB infection in patients with HIV, the frequency of PNT may increase, although this has not yet occurred, due possibly to effective public health measures to identify, isolate, and treat active cases of TB.

International

PNT is an uncommon disorder even in populations with a high prevalence of TB, occurring in less than 5% of active TB cases. In the literature, 91 cases were reported during a 17-year period in South Africa in 1974. In addition, 12 cases from a period of longer than 30 years in England were reported in 1986. In the latter study, most patients were immigrants and had presumably acquired the infection outside of England.

Mortality/Morbidity

The condition typically follows a prolonged and relapsing course lasting years, although spontaneous resolution has been reported. Significant varioliform scarring is a sequela, and progression to lupus vulgaris has been observed. An association with Takayasu arteritis of the aortic arch has also been documented.

Sex

Females seem to be at a slightly increased risk for developing this disorder.

Age

Children and young adults are more susceptible to this condition than other people. In the 1974 study from South Africa, two thirds of the patients were younger than 30 years.

Clinical

History

• The characteristic lesions are small, erythematous, inflammatory papules that undergo central ulceration and heal spontaneously within weeks, leaving a varioliform scar.
• Lesions arise in symmetric crops, typically with an acral predilection. Characteristically, lesions develop over the extensor surfaces, particularly the knees, the elbows, and the dorsum of the hands and the feet, although widespread involvement may be present.
• New lesions form as older lesions resolve, giving the eruption a polymorphous appearance.
• Oral lesions have not been reported to date.
• PNTs have been reported to coexist with lesions of erythema induratum, as well as lichen scrofulosorum. In several reports, cutaneous lesions resolved with appropriate anti-TB therapy.

Physical

• Primary lesion: The characteristic initial lesions are 2- to 8-mm, erythematous papules that become pustules and undergo central ulceration forming hemorrhagic-crusted papules.
• Distribution: Lesions arise in symmetric crops, typically with an acral predilection. Characteristically, lesions develop over the extensor surfaces, particularly the knees, the elbows, and the dorsum of the hands and the feet, although widespread involvement may occur. Involvement of the glans penis has also been reported.
• Color: Hyperpigmented to erythematous papules with central crusting are seen early, and the lesions generally heal with scarring.
• Lymph nodes: In one study, as many as one third of the cases were associated with cervical lymphadenopathy, and some patients developed scrofuloderma.

Causes

The eruption is a form of an exaggerated host immunologic response to a mycobacterial infection involving the cutaneous vessels. Active TB is reported in as many as 40% of patients.

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