Tinea corporis (ringworm) is the name used for infection of the trunk, legs or arms with a dermatophyte fungus.
In different parts of the world, different species cause tinea corporis. In New Zealand, Trichophyton rubrum (T. rubrum) is the most common cause. Infection often comes from the feet (tinea pedis) or nails (tinea unguium) originally. Microsporum canis (M. canis) from cats and dogs, and T. verrucosum, from farm cattle, are also common.
Clinical features of tinea corporis
Tinea corporis may be acute (sudden onset and rapid spread) or chronic (slow extension of a mild, barely inflamed, rash). It usually affects exposed areas but may also spread from other infected sites.
Acute tinea corporis presents as itchy inflamed red patches and may be pustular. The cause is often infection by an animal (zoophilic) fungus such as M canis.
Chronic tinea corporis tends to be most prominent in body folds (spreading from tinea cruris). T. rubrum is the most common cause. If widespread, the condition tends to be stubborn to treat and prone to recurrence. This is possibly due to a decreased natural skin resistance to fungi or because of reinfection from the environment.
The term ringworm refers to round or oval red scaly patches, often less red and scaly in the middle or healed in the middle. Sometimes one ring arises inside another older ring.
Kerion is an inflamed fungal abscess. It presents as a boggy mass studied with pustules, often with satellite spots. It is often confused with a large boil or carbuncle or a tumour such as a skin cancer.
Majocchi granuloma describes tinea corporis involving the hair follicles resulting in pustules and nodules.
Tinea imbricata is due to T. concentricum and occurs in the Pacific Islands and other tropical areas. It results in brown scaly concentric rings.
Non-fungal conditions resembling tinea corporis include:
- Seborrhoeic dermatitis
- Discoid eczema
- Lichen simplex
- Contact allergic dermatitis
- Pityriasis rosea
Diagnosis of tinea corporis
The diagnosis of tinea corporis is confirmed by microscopy and culture of skin scrapings.