Fig. 6.26 A-D. Actinomadura pelletieri is an aggressive fungus: in the foot, multiple small bones are usually affected and show numerous small bony cortical defects and an exuberant periosteal reaction. The average diameter of the holes is 2 mm but they may be obscured as the periosteal and new bone formation develop. The end result shows extensive destruction. A Soft tissue swelling, with multiple sinuses visible around infection of the first four metatarsals and adjoining tarsal bones. B A. pelletieri can extend from the foot into the tibia and fibula, but there is still the same periosteal new bone formation with multiple small 2-mm punched out lesions. As the joint is involved, fusion will occur, as in this case from West Africa. (Courtesy of the late Professor W. B Cockshott) C, D The end result of A. pelletieri infection. Multiple areas of bone destruction with many small holes, joint destruction, and bony fusion. Many patients come to hospital for some other illness rather than their abnormal foot: they have had it so long that they have got used to it, and the need for amputation may be an unwelcome surprise.

The best way to start this section is with an extract from Medical Mycology by Drs. Kwon-Chung, and Bennett (Lea and Febiger, Philadelphia, 1992): "The changing terminology for mucormycosis and many of its causative agents has complicated their retrieval from the literature and confused clinicians ... the name mucormycosis has been used extensively and is retained as a medical subhead for indexing ... the older term, phycomycosis is unacceptable because the class of phycomycetes no longer exists. The more recent term zygomycosis ... is usually too imprecise to be helpful (for an individual patient)".
It seems probable that not only clinicians are confused?

Synonyms

Mucormycosis, Phycomycosis. Entomophthoromycosis. It is likely that many cases of entomophthoromycosis have been described under headings of infection with mucormycosis (see under definition).

Definition

Zygomycosis is the general term for an infection caused by pathogenic zygomycetes of the orders Murocales and Entomophthorales.

Mucormycosis is a systemic fungal infection caused the genera Rhizopus, Mucor, or Absidia. Less often it is due to Cunninghamella or Saksenaea.

Entomophthoromycosis is infection caused by one of the Entomophthorales, usually Basidiobolus haptosporus or Conidiobolus coronatus, and very rarely Conidio bolus incongruus. These infections have epidemiological, clinical, and pathological differences from mucormycosis. It seems very possible that clinical and imaging descriptions have not made a clear differentiation, which may be more important therapeutically than for other reasons.

Geographic Distribution

Zygomycetes are found worldwide: infections have been reported from the Indian subcontinent, Africa, South America, Asia, Europe, and the United States.

Epidemiology and Pathology

The zygomycetes are the common molds found on bread, cheese, and fruit. They are also present in decaying vegetation.

Mucormycosis seldom occurs in healthy individuals, although some have been infected while apparently otherwise healthy. It is most common in patients who are immunocompromised for any reason, including diabetes, renal failure, leukemia, the reticulosis, and malnutrition. Mucormycosis is rare in AIDS patients, but both may occur in intravenous drug users. Skin and soft tissue infection has followed local trauma. Intravenous drug abuse is another common factor. Several infections have been linked with contaminated adhesive bandages/tape which have been left in place too long so that the underlying skin has become damaged. Organ transplantation and clinical immunosuppression for any reason increase the risk of infection.

The Entomophthorales are found in the alimentary tract of many amphibians, reptiles, horses, dogs, and chimpanzees but few are clinically infected. A significant difference which affects pathogenicity is that, unlike the members of the Mucorales, the organisms of the Entomophthorales tend not to invade the wall and lumen of blood vessels (although a few cases of disseminated infection have been recorded). Because vascular invasion is not a feature of the entomophthomycoses, neither septic thrombosis nor infarction and the subsequent necrosis are observed as with mucormycoses. The entomophthomycosis tend to be characterized by indolent local infections, in contrast to the usually quickly disseminating mucormycosis. Entomophthora coronata almost always affects only the upper respiratory tract. The hyphae of entomophthoromycoses are septate, while those of mucormycetes are nonseptate; in addition, the hyphae in entomophthomycoses often are enclosed by an eosinophilic sheath (Splendore-Hoeppli phenomenon) not seen in the mucormycoses (Fig. 6.27).

In other respects the infections are similar, with central abscesses surrounded by numerous eosinophils. Biopsy is the best way to establish the diagnosis because serology is unreliable.