Subcutaneous Mycoses

Subcutaneous mycoses are fungal infections of the dermis, subcutaneous tissue, and sometimes bone that are introduced when fungi living in soil or on plants are inoculated through the skin by trauma. Because the fungi must be implanted rather than inhaled or merely colonising the surface, these infections tend to be chronic, localised, and associated with environmental and occupational exposure.

Definition

Fungal infections of the dermis, subcutaneous tissue, and occasionally underlying structures, acquired by traumatic implantation of environmental fungi through the skin; they characteristically remain localised and follow a chronic, slowly progressive course.

Scope

The topic covers the classic implantation mycoses — sporotrichosis, chromoblastomycosis, and eumycetoma — together with related entities, emphasising their shared mechanism of traumatic inoculation and their chronic course. It is a reference overview of the category and does not provide individualised diagnostic or therapeutic recommendations.

Key concepts

• Traumatic implantation as the portal of entry
• Environmental (soil and plant) fungal reservoirs
• Sporotrichosis and lymphocutaneous spread
• Chromoblastomycosis and muriform (sclerotic) bodies
• Eumycetoma and grain formation
• Chronic, localised, granulomatous disease
• Neglected tropical disease context

Mechanisms

Subcutaneous mycoses begin when a fungus that normally lives saprophytically in soil, wood, or vegetation is pushed beneath the skin by a thorn, splinter, or other minor wound. The organism then establishes a chronic infection in the dermis and subcutis, often eliciting a granulomatous host response. Sporothrix species typically spread along lymphatic channels to produce the lymphocutaneous pattern (Kauffman, 2007); the agents of chromoblastomycosis form characteristic muriform (sclerotic) bodies in tissue (Queiroz-Telles, 2017); and in eumycetoma the fungus aggregates into grains within abscesses and draining sinuses that can extend to bone (Zijlstra, 2016). Their intermediate tissue depth — below the keratin but usually not disseminating — defines their place in the depth-and-distribution scheme.

Clinical relevance

Subcutaneous mycoses matter clinically because they are chronic, can be disfiguring or disabling, and are strongly tied to environmental and occupational exposure, so a history of skin trauma in an endemic setting is part of recognising them. This entry summarises the category for reference and is not guidance for managing any individual case.

Epidemiology

These infections occur worldwide but are concentrated in tropical and subtropical regions and among people with outdoor and agricultural exposure who sustain minor skin trauma; chromoblastomycosis and mycetoma in particular are recognised neglected tropical diseases with a marked burden in rural populations of endemic zones (Queiroz-Telles, 2017; Zijlstra, 2016).

History

Sporotrichosis was described at the close of the nineteenth century and became the prototype implantation mycosis, while chromoblastomycosis and mycetoma were characterised over the twentieth century and codified in medical-mycology texts such as Rippon's Medical Mycology (Rippon, 1988). Mycetoma's later formal recognition as a neglected tropical disease reflected growing attention to its burden in endemic regions (Zijlstra, 2016).

Seminal works

• kauffman-2007
• queiroz-telles-2017
• zijlstra-2016

Frequently asked questions

How are subcutaneous mycoses acquired?

They are acquired by traumatic implantation — environmental fungi from soil or plants enter through a minor skin wound, such as a thorn prick, rather than by inhalation or surface colonisation.

Why are subcutaneous mycoses usually chronic and localised?

The fungi are introduced into the subcutaneous tissue and provoke a slow, granulomatous response that tends to stay confined to the inoculation site and surrounding tissue rather than disseminating widely.