Unusual variants of mycosis fungoides – NIH

~Content Source

Conventional presentations of mycosis fungoides may be diagnostically challenging, particularly in light of the controversial boundaries defining the disease. Variant presentations of this cutaneous T-cell lymphoma add a further layer of complexity, requiring a sophisticated and informed perspective when evaluating lymphoid infiltrates in the skin. Herein we discuss well-defined (WHO-EORTC) variants pagetoid reticulosis, granulomatous slack skin and folliculotropic mycosis fungoides as well as less well-defined morphologic/architectural variants, and divergent immunohistochemical presentations of this typically indolent T-cell lymphoproliferative disease.

Fungi and Human Pathogenesis

~ Content Source – Neal Chamberlain

Humans have a high level of innate immunity to fungi and most of the infections they cause are mild and self-limiting.

This resistance is due to:

  • 1. the fatty acid content of the skin.
  • 2. the pH of the skin, mucosal surfaces and body fluids.
  • 3. Epithelial cell turnover.
  • 4. Normal flora.
  • 5. Transferrin.
  • 6. Cilia of the respiratory tract.

When fungi do pass the resistance barriers of the human body and establish infections, the infections are classified according to the tissue levels initially colonized.

A. Superficial mycoses– infections limited to the outermost layers of the skin and hair.

B. Cutaneous mycoses– infections that extend deeper into the epidermis, as well as invasive hair and nail diseases.

These diseases are restricted to the keritinized layers of the skin, hair, and nails. Unlike the superficial mycoses, host immune responses may be evoked, resulting in pathologic changes expressed in the deeper layers of the skin. The organisms that cause these diseases are called dermatophytes. These diseases are often called ringworm or tinea. All the following diseases are causes by MicrosporumTrichophytonand Epidermophytonwhich comprise 41 species.

C. Subcutaneous mycoses- infections involve the dermis, subcutaneous tissues, muscle, and fascia. These infections are chronic and are initiated by trauma to the skin. These infections are difficult to treat and may require surgical intervention.

D. Systemic mycoses- infections that originate primarily in the lungs and may spread to many organ systems. These organisms are inherently virulent. All but Cryptococcus are dimorphic fungi.

Histoplasma capsulatum– Ohio and Mississippi river valleys, Yeast cells in tissue, Tuberculate macroconidia in mycelial phase.

Blastomyces dermatitidis– Ohio and Mississippi river valleys, Broad Base Budding yeast in tissue, Mycelia= microconidia

Coccidioides immitis– Southwestern US. Spherule in tissue, barrel-shaped Arthroconidia in mycelia phase.

Cryptococcus neoformans– Only yeast phase but unusual in that the cells are encapsulated as demonstrated by an India Ink stain.

E. Opportunistic mycoses– infections of patients with immune deficiencies who would otherwise not be infected. Ex. AIDS, altered normal flora, diabetes mellitus, immunosuppressive therapy, malignancy.

Candidiasis– Candida albicans– Creamy growth on various body surfaces. ex. mouth, skin, vagina. Budding yeast. Form pseudohyphae in tissue. Germ tube when grown in serum.

Aspergillosis– Aspergillus niger.

For more content download PDF Doc – Fungal Infections

Zygomycetes in Human Disease

Content Source-NCBI

The Zygomycetes represent relatively uncommon isolates in the clinical laboratory, reflecting either environmental contaminants or, less commonly, a clinical disease called zygomycosis. There are two orders of Zygomycetes containing organisms that cause human disease, the Mucorales and the Entomophthorales. The majority of human illness is caused by the Mucorales.

Organisms of the class Zygomycetes were first noted to cause disease in humans in publications from the 1800’s.

PDF Doc – 66 pages. – Zygomycetes-in-Human-Disease

Opportunistic Mycoses

Opportunistic mycoses are infections due to fungi with low inherent virulence which means that these pathogens constitute an almost limitless number of fungi.  These organisms are common in all environments.

The disease equation:

Number of organisms  x  Virulence = Disease
Host resistance

With opportunistic infections, the equation is tilted in favor of “disease” because resistance is lowered when the host is immunocompromised. In fact, for the immunocompromised host, there is no such thing as a non-pathogenic fungus.

The fungi most frequently isolated from immunocompromised patients are saprophytic (i.e. from the environment) or endogenous (a commensal).  The most common species are Candida species, Aspergillus species, and Mucor species.

The upward trend in the diagnoses of opportunistic mycoses reflects increasing clinical awareness by physicians, improved clinical diagnostic procedures and better laboratory identification techniques. Another important factor contributing to the increasing incidence of infections by fungi that have not been previously known to be pathogenic has been the rise in the number of immunocompromised patients who are susceptible hosts for the most uncommon agents. Patients with primaryimmunodeficiencies are susceptible to mycotic infections particularly when cell-mediated immunity is compromised. In addition, several types of secondary immunodeficiencies may be associated with an increased frequency of fungal infections.

OPPORTUNISTIC MYCOSES – PDF

Content Source-Microbiology and Immunology On-line | University of South Carolina School of Medicine