Subcutaneous Mycoses

Subcutaneous Mycoses

The fungal infections are characterized by development of lesions at the site of infection by the traumatic inoculation in the subcutaneous tissues. Examples are Mycetoma, Sporotrichosis, Chromoblastomycosis and Rhinosporidiosis.

Mycetoma

Mycetoma is a slowly progressive, chronic granulomatous infection of skin and subcutaneous tissues with involvement of under lying fasciae and bones usually affecting the extremities. Mycetoma is commonly called Madura foot or Maduramycosis (Figure 9.7). They are classified into two categories, namely eumycetoma cased by fungi and actinomycetoma caused by higher bacteria of class actinomycets.

Pathogenesis and Pathology

The causative agent of Mycetoma is commonly present in saprobic soil source and is transmitted by accidental trauma by thorns or by injury into the subcutaneous tissue. It is common among farmers with minor trauma and abrasions of the skin. Use of wicks for removal of earwax is responsible for Mycetoma of the ear.

HOTS: Is mycetoma occupational disease?

Classification of Mycetoma

Mycetoma is classified on the basis of the causative agent. Aerobic actinomycetes causes actinomycetoma whereas hyaline and phaeoid fungi cause eumycetoma.

Clinical Features

The clinical entity depends upon the age of the lesions and to size, shape and color of the grains. The painless localized swollen lesions with purulent fluid lead to the secondary bacterial infections. Important features of Mycetoma are as follows:

i. Tumor like swelling.

 ii. Multiple draining sinuses.

iii. Presence of grains or granules in sinuses..

Laboratory Diagnosis

i. Samples

The clinical samples collected in Mycetoma is usually grains, pus exudates or biopsy.

a. Direct Examination

Grams staining, modified Ziehl – Neelson staining, LPCB and KOH wet mount are used to visualize the organisms.

The grains should be washed, crushed and cultured on different media. Crushed grains are examined (Figure 9.8a).

KOH mount

Eumycotic grains show thick 2–6 µm hyphae with large globose swollen cells with or without chlamydospores. Actinomycotic grains show thin filaments of 0.5–1 µm with coccoid or bacillary forms.

Gram stain

Actinomycetoma grains show Gram-positive branching filamentous bacteria with branches (Figure 9.8b).

Ziehl - Neelson stain

Nocardia species show red pink acid fast filamentous bacteria.

b. Culture

Crushed grains are washed several times with normal saline without antibiotics and inoculated on to Sabouraud dextrose agar, blood agar, Lowenstein -Jensen media and brain-heart infusion agar. The plates are incubated at 25°C, 37°C and 44°C for various organisms (Figure 9.8c).

ii. Treatment

1. Ketoconazole 200 mg and Itraconazole 100mg are given for 8–24 months to treat eumycetoma.

2. Sulfonamides, tetracylines, streptomy-cin, amoxicillin are administered to treat actinomycetoma.