++
Zygomycosis is an umbrella term
for all diseases caused by fungi of the class Zygomycetes. The more
common term mucormycosis refers to a group of invasive
mycoses caused by members of the order Mucorales within the class
Zygomycetes.1Rhizopus species
are the most commonly isolated agents of mucormycosis.2 The
Mucorales are distributed worldwide and commonly grow in decaying organic matter.3 Although
exposure to the airborne spores of these thermotolerant, rapidly
growing fungi is universal, human disease is infrequent and is indicative
of a serious underlying predisposing condition.4 Diabetes
mellitus, particularly diabetic ketoacidosis, is the most common
predisposing condition in patients with mucormycosis.2,5 Underlying
disease accompanied by acidosis, such as uremia, malnutrition,6 and
congenital metabolic aciduria,7 may also predispose
to mucormycosis. Additional
risk factors include neutropenia,8 hematological malignancies,9 burns,10 prematurity,11 corticosteroid
therapy,12 solid-organ transplantation,13 bone
marrow transplantation,14 and deferoxamine/desferrioxamine
therapy for management of iron and aluminum overload states.15
++
Infection in humans most commonly occurs following inhalation
of the spores of Mucorales into the respiratory tract.4 Spores may
also be ingested or introduced directly into abraded skin.16 Germination
of spores occurs with hyphal proliferation and invasion of tissue.
Infection may spread by direct extension and hematogenous dissemination. Regardless
of the tissue involved, the pathologic hallmark of mucormycosis
is hyphal invasion of blood vessels with resultant hemorrhage, thrombosis,
infarction, and production of black, necrotic debris.6,17 The
reasons these fungi target the vasculature are unknown.
++
The mechanisms that account for the increased susceptibility
to mucormycosis in different patient groups remain incompletely understood.
Neutrophils and macrophages are important components of the host
response to Mucorales.18,19 Thus, defects in their
function likely contribute to the pathogenesis of mucormycosis.
Iron is an important growth factor for these fungi; hence, interactions
between iron molecules and transferrin have been postulated to play
a role in predisposing deferoxamine-treated patients to the development
of mucormycosis.20 Because these fungi metabolize
ketones and grow optimally at an acid pH,21 the metabolic
conditions encountered in ketoacidotic hosts may enhance their growth.
++
Clinical Manifestations
++
The clinical manifestations of mucormycosis are classified by
site of involvement into rhinocerebral, pulmonary, cutaneous, gastrointestinal,
disseminated, and miscellaneous infections.1 Rhinocerebral
infection occurs most frequently and typically presents as facial
pain, nasal congestion, and headache in a poorly controlled diabetic
patient.22,23 From the nasal mucosa and paranasal
sinuses, Infection may spread to the orbit, resulting in orbital
cellulitis, paresis of extraocular muscles, and proptosis. Further
extension into the cerebral vasculature and brain can lead to cavernous
sinus thrombosis, brain infarcts, and focal neurologic deficits.24
++
Most cases of pulmonary mucormycosis have occurred in neutropenic
hosts, especially those receiving chemotherapy for leukemia and lymphoma.25 Clinically, These
patients present with unremitting fever and dyspnea. The chest roentgenogram
may show patchy consolidation and ...