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Atypical mycobacterial infections are increasingly important in
immunosuppressed patients as well as in healthy hosts.
Visit:
Atypical Mycobacterial Infection ;Mycobacterium Leprae Inf.
;
Mycobacterium Avium Intracellulare
;
Mycobacterium ulcerans Inf.
;
Mycobacterium tuberculosis
; Mycobacterium Kansasii
;
The atypical
mycobacterium that most commonly affects the skin is Mycobacterium
marinum.
The infection
should be suspected upon the presence of ulcers, nodules or chronic
plaques and a history of contact with fresh or salt water.
The disease is typically acquired
following contact with infected water and in many instances has been
described following the cleaning of fish tanks with minor penetrating
trauma being important in the pathogenesis.
The infection usually involves
superficial tissues of the distal aspect of the upper or lower limbs.
Deeper soft tissue may also be
involved. In some cases tenosynovitis may occur.
There may be primary synovial
involvement or secondary to skin involvement.
Cutaneous nodules, sometimes with a
lymphatic distribution reminiscent of
sporotrichosis
, are often the presenting sign and
some patients have a history of several years of widespread warty
lesions clinically resembling sporotrichosis.
Dissemination
of Mycobacterium marinum-infection is a rare condition which occurs
mainly in immunocompromised patients and can be life-threatening.
Considerable time may elapse before the
diagnosis is made, patients often being treated unsuccessfully for
various conditions. This highlights the importance of a detailed
history including occupational and recreational exposure and recent
travel.
Fish tank
granuloma:
Granulomatous lesions of the skin and tendon sheaths after exposure to
fish tank or aquarium water are frequently caused by non-tuberculous
so-called atypical mycobacteria. Mycobacterium marinum is the species
most often isolated from such lesions. Fish tank granuloma seems to be
a rare sporadic human disease that is often misdiagnosed.
Histopathological examination of
involved synovium in patients with disease principally in this site
shows hypertrophy and hyperplasia of synovial lining cells together
with a fibrinous exudate. The presence of granulomas is variable.
Granulomas, if present, tend to be well
defined and non-caseating, but poorly defined granulomatous foci may
be present in some cases, and in others suppurative inflammation may
predominate.
Hyperkeratosis and
pseudoepitheliomatous hyperplasia of the epidermis may be found in
cutaneous infections.
There is a reciprocal relationship
between the expression of suppurative inflammation and granulomatous
changes.
Such a relationship might be expected,
but a combination of granulomatous inflammation and acute inflammation
is a key feature of subcutaneous and deep fungal infections.
The varied histopathological reactions
to M. marinum infection are difficult to explain but could be related
to its growth rate, which is between 5 -14 days, falling intermediate
between M. tuberculosis (12 - 28 days) and the rapid growers (M.
abscessus, M. chelonae and M. fortuitum) with a rate of 3 - 7 days.
Acid-fast bacilli are rarely identified
in tissue sections reinforcing the need to culture tissue for species
identification.
Mycobacterium
marinum infections are emerging infections related to fish tank hobby.
Because of the severity of the cases with spread of infection,
clinical awareness of M. marinum infection and its associated risk
factors is important so that the diagnosis can be made and therapy can
be initiated promptly.
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