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CLINICAL
FEATURES:
A sixty-year-old
woman developed a red to purple vegetative, focally eroded plaque
on the volar aspect of her right thumb (Fig
1). She was a farmwife who tended horses and cattle. A biopsy
was performed.
HISTOPATHOLOGIC
FEATURES:
There
is variable hyperkeratosis and parakeratosis surmounting an irregular
psoriasiform to vegetative epidermis (Fig.
2). The underlying dermis contains an infiltrate of neutrophils
and lymphocytes along with focal collections of histiocytes. The
neutrophils collect, form subepidermal pustules focally, and intraepidermal
abscesses are identified (Fig.
3). Periodic acid-Schiff reagent stain with diastase digestion,
methenamine silver stain and initial acid fast stain reveal neither
filamentous bacteria, fungi nor myco-bacteria. Repeat acid fast
stain revealed rare acid fast bacilli deep within the specimen (Fig.
4).
DIAGNOSIS:
Primary
mycobacterium marinum infection.
DISCUSSION:
The
acid-fast bacilli are longer and broader than in bovine tuberculosis.
Group 1 photochromigen mycobacteria are present in brackish, stagnant
water. The patient likely acquired her infection from watertroughs,
which she cleaned for her horses. Primary inoculation atypical mycobacterial
infection is an occupational hazard for salt-water fishermen. Outbreaks
have been associated with swimming pool exposure. Aquariums are
now a common source of infection. A nodule develops at the site
of inoculation that often suppurates or that may ulcerate. The nodule
may have a purulent vegetative surface. Sporotrichoid may develop
along the lymphatic vessels extending up the extremity. The histopathologic
features are characteristic. The pseudoepithiomatous hyperplasia
may be even greater than observed here simulating carcinoma. The
early neutrophilic stage evolves into a fibrotic granulomatous stage.
The mycobacteria may be identified in the early stage of infection
but it is often impossible to demonstrate them in the late stage
granulomatous. This particular case illustrates that multiple acid
fast stains may be necessary in order to demonstrate the organisms.
Immunohistochemical studies and polymerase chain reaction have been
used to identify the organisms in tissue. The differential diagnosis
of such lesions includes tuberculous chancre, cat scratch disease,
tolaremia, sporotrichosis, actinomycosis, and deep fungal infection.
Culture and special stains on tissue sections are required to be
certain of the diagnosis. This is particularly important because
Mycobacterium marinum grows slowly and thus requires weeks to identify.
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