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MYCOBACTERAIL INFECTIONS

Tuberculosis of the skin

Infection of the skin by Mycobacterium tuberculosis or M. bovis occurs in a variety of patterns. Inoculation of the skin may occur from an exogenous source (e.g. another's saliva) and cause tuberculosis verrucosa cutis (Figs 24.47 and 24.48). Autoinoculation (e.g. from the patient's own saliva) may lead to orificial tuberculosis. Extensive ulceration of the nasal and auricular cartilage may occur. Tumorous growths and hypertrophic forms may also occur. Extension from underlying infected lymph nodes may cause scrofuloderma. Hematogenous spread may cause acute miliary tuberculosis or in some cases lupus vulgaris (discussed shortly).

    Tuberculosis (TB) of the skin has been rare in developed countries for many years, other than in immigrants from areas where vaccination has not been routine, but an increased incidence has occurred as a result of HIV infection and the AIDS epidemic.

    Diagnosis of TB of the skin using conventional methods is often unsatisfactory: special stains and culture of tissue (e.g. on Löwenstein– Jensen medium) often result in repeated false negative results. Polymerase chain reaction (PCR) technology to detect genome sequences of M. tuberculosis in biopsied tissue can establish the diagnosis in just a few days.

    Various reaction patterns or ‘tuberculids' are described, including lichen scrofulosorum, papulonecrotic tuberculide, and erythema induratum (Bazin disease). On the basis of PCR technology, most cases of the last of these are best viewed as a non-TB related nodular vasculitis.

Figure 24.47 Tuberculosis verrucosa cutis. A chronic, warty plaque on the hand, knees, ankles, or buttocks (as shown here) is characteristic of this infection caused by Mycobacterium tuberculosis. Inoculation may have occurred from the patient’s own saliva, another’s saliva (e.g. sitting on spit), or from work (e.g. a pathologist with a prosector’s wart).

Figure 24.48 (a,b) Tuberculous abscess and disseminated skin lesions. This patient presented with swelling of the wrist, malaise, and skin nodules. The wrist lesion was fluctuant and extended under the flexor retinaculum with a bilobed shape. Forty milliliters of viscous white pus were aspirated. Mycobacteria were present in the pus and in the biopsy of a skin lesion, and were identified as Mycobacterium tuberculosis.

Lupus vulgaris

This disease represents an infection by M. tuberculosis in a patient with moderate to high immunity, and may have developed from local inoculation, or lymphatic or hematogenous spread. For many years, it has been the commonest form of cutaneous TB in developed countries.

    A hyperkeratotic, crusted, granulomatous plaque (or plaques) occurs on the face or at a site of accidental inoculation (Figs 24.49 and 24.50). Ulceration, deformity, and development of squamous cell carcinoma may occur. The color may be red-brown or translucent. An apple jelly color is seen on diascopy (pressure to remove the blood with a glass slide). The striking feature is the chronicity of many cases; the last two cases seen by one of the authors were of 50 years' and 80 years' duration (on the knee and on the buttock, respectively); as a result of this, the patient may have been told decades earlier that ‘nothing can be done' or may have had prolonged unsuccessful treatment for a ‘stubborn plaque of psoriasis'.

    Work-up should include tuberculin testing, chest radiography, and skin biopsy. PCR of paraffin-embedded tissue has been used successfully to detect the organism and establish the diagnosis.

    Early lesions may be surgically excised. Antituberculosis combination therapy (e.g. isoniazid, rifampin, and pyrazinamide) should be given.

Figure 24.49 Lupus vulgaris. A hyperkeratotic, crusted, granulomatous plaque (or plaques) on the face or elsewhere is characteristic. An apple jelly color is seen on diascopy (pressure to remove the blood with a glass slide).

Figure 24.50 Lupus vulgaris. This patient developed a crusted red area of skin on her knee after she tripped and fell while running to an air raid shelter during World War II. It gradually expanded and was treated as an area of psoriasis until she sought a dermatologic opinion and was given the correct diagnosis almost 50 years later.

Atypical mycobacterial infection

Etiology and pathogenesis

A variety of atypical mycobacteria infect the skin. M. marinum is probably the most common and causes the classic fish tank granuloma. The rapidly growing mycobacteria, M. fortuitum and M. chelonei , may cause postsurgical infection in the immunocompetent patient as a cellulitis or as a postinjection abscess. M. scrofulaceum causes cervical adenitis in children. The M. avium complex comprises two very similar species: M. avium and M. intracellulare . M. avium skin infection was rare until the AIDS epidemic.

Clinical

The commonest infection is the fish tank or swimming pool granuloma. If acquired from an aquarium, the dominant hand is typically affected. A violaceous, crusted, or hyperkeratotic papulonodule develops on the dorsal surface of the hand or finger, often over a knuckle (Figs 24.51 and 24.52). If acquired from a pool, any site of trauma may be affected. Any hobbies or occupations that bring the patient in contact with fish are predisposing factors. For lesions elsewhere, a history of trauma is often present (Fig. 24.53). The lesions may go undiagnosed for years. The patient is often treated with oral antibiotics for several courses until the correct diagnosis is made. Sporotrichoid spread (a form of lymphadenitis in skin lymphatics) may occur (Fig. 24.54).

    Mycobacterium fortuitum is a common cause of infections of the leg after pedicure (Fig.24.55). The woman usually presents with one to several inflammatory nodules of the leg soon after obtaining a pedicure.

Figure 24.51 Atypical mycobacterial infection. This fish tank granuloma developed several months after the patient cleaned his aquarium. Any hobbies or occupations that bring the patient in contact with fish are predisposing factors to this infection by Mycobacterium marinum.

Figure 24.52 Atypical mycobacterial infection. This patient accidentally stabbed his fingertip with the screwdriver that he used to adjust the thermostat in his tropical fish tank.

Figure 24.53 Atypical mycobacterial infection: primary inoculation site. This young man developed slowly expanding inflammation and ulceration on the lower leg at an area of minor injury. Pyoderma gangrenosum was considered, but histologic features were granulomatous, and a diagnosis of atypical mycobacterial infection was favored. Although cultures were negative, the lesion responded to minocycline with no subsequent recurrence. Soil-derived mycobacteria may be very difficult to identify due to their specific temperature requirements in culture.

Figure 24.54 Nodular lymphangitis. Tender, inflamed nodules progressing up the arm, originating from a traumatic injury on the hand, so-called sporotrichoid spread, is characteristic of nodular lymphangitis, also called lymphocutaneous syndrome (same patient as in Fig. 24.52). The most common atypical mycobacterium to spread in a sporotrichoid fashion is Mycobacterium marinum, as shown here. Other infectious agents that may be found include Leishmania, Nocardia brasiliensis, Francisella tularensis, and Sporothrix schenckii.

Figure 24.55 Mycobacterium fortuitum is a common cause of infections of the leg after pedicure. The patient, usually a woman, presents with one or more inflammatory papules and/or nodules on the lower legs. The lesion pictured here was the largest of four inflammatory nodules on the leg of a young woman. Culture showed M. fortuitum.

Differential diagnosis

Most lesions are treated on the basis of having a simple infected wound or abscess, or a foreign body granuloma. More chronic lesions may be confused with warts or knuckle pads. A solitary lesion might rarely be confused for a neoplasm. Typically, the appearance of sporotrichoid spread suggests the presence of atypical mycobacteria or other uncommon infections (Table 24.6).

    If a patient presents with a lesion suspicious for atypical mycobacterium infection, then biopsy for histopathology, special stains, and culture (bacterial, fungal, and acid-fast bacilli) should be done. The laboratory staff should be alerted to look for an atypical mycobacterium, as they require special culture conditions, but a deep fungal infection or other unusual bacteria should also be excluded when performing cultures.

Treatment

Whenever possible, the specific organism should be cultured and sensitivities determined. In the absence of this, certain agents may be tried empirically. Clarithromycin (e.g. 250mg twice a day) has been shown to be very active against the atypical mycobacteria. Minocycline or doxycycline (100mg twice a day), tetracycline (500mg four times a day), or co-trimoxazole (trimethoprim and sulfamethoxazole) twice daily may be employed. In one study, ethambutol (25mg/kg per day) plus rifampin (600mg/day) was slightly more successful than minocycline (100mg twice a day). All subgroups of atypical mycobacteria are susceptible to intravenous amikacin. If medical treatment is employed, it should be continued until the lesion has resolved clinically.

White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.