skin health

erythrasma

What is erythrasma?

Erythrasma is a chronic dermatological infection that mainly affects intertriginous regions of the body (skin folds), manifesting itself as a strong macular eruption (similar to a mycosis).

The microorganism involved in the appearance of this condition is Corynebacterium minutissimum, a bacterium belonging to the autochthonous bacterial flora, but which can potentially become pathogenic, in favorable conditions for its proliferation.

The sites most affected by the manifestation of erythrasma are the interdigital areas (the lesions appear as macerations) and the inguinal region (crural area, inner part of the thighs). Infection affects less commonly: axillae, inframammary fold, abdomen (periombelical region) and intergluteal groove.

Erythrasma is usually a benign condition. However, it can be invasive in subjects prone to infection and immunocompromised (in these individuals the susceptibility is secondary to the presence of other related infections, such as endocarditis, pyelonephritis, meningitis ...).

Due to the association of erythrasma with other dermatological conditions, such as punctate keratolysis or axillary trichomicosis, all the folds and extremities of the body (hands and feet) must be analyzed during diagnosis.

From an epidemiological point of view, the global incidence is around 4%. This infection affects both sexes and is distributed worldwide, although it is more widespread in subtropical and tropical areas.

Pathophysiology

In favorable conditions, such as heat and humidity, Corynebacterium minutissimum proliferates in wet areas, especially in the folds of the skin: it invades a portion of the stratum corneum which, as a result of the infection, appears as thickened. These microorganisms can be detected in the intercellular spaces, as well as within the cells. The skin spots examined at Wood's lamp take on a coral red color, as a consequence of the characteristic production of porphyrin by Corynebacterium minutissimum : the presence of this metabolite provides diagnostic evidence of the presence of the pathogen infection.

Signs and Symptoms

To learn more: Symptoms Erythrasma

The erythrasma appears with dark, reddish-brown spots, well defined and associated with the appearance on the skin of fine flakes that give it a scaly (wrinkled) appearance.

The appearance of these spots is usually limited to the folds of the body that are naturally moist and occluded (groin, armpits, skin folds, etc.). In rare cases, erythrasma can also spread to the trunk and limbs.

Infection is often asymptomatic, but may be associated with mild itching. Symptoms that commonly appear are:

  • Lichenification : pathological thickening of the skin manifested by plaques, flaking, with accentuated skin design.
  • Hyperpigmentation : local alteration of skin color. Erythrasma is associated with the appearance of brown-red spots that are generally small.

Moreover, the strong macular eruption can be associated with other fungal infections: for this reason the doctor performs a differential diagnostic analysis, which allows to discriminate the erythrasma among similar pathologies, which are progressively excluded based on the presence or absence of other symptoms and clinical signs. For example: the KOH test, generally performed for the diagnosis of Candida albicans, is negative.

Causes

The causative agent of erythrasma is Corynebacterium minutissimum, a normal member of the skin flora. The main features of the bacterium are:

  • Gram positive, non sporogenic diphtheroid, aerobic, positive catalase;
  • it ferments: glucose, dextrose, sucrose, maltose and mannitol.

The predisposing factors for the infection are the following:

  • excessive sweating (hyperhidrosis);
  • sensitivity of the skin barrier;
  • obesity;
  • Diabetes mellitus;
  • hot weather;
  • poor hygiene;
  • old age;
  • immunocompromised states.

Differential diagnosis

The differential diagnosis tends to exclude the various similar manifestations in a given subject, through the exact understanding of the set of symptoms and signs found during the clinical examinations.

The symptoms perceived by the patient suffering from erythrasma can be confused with pathologies that show similar dermatological manifestations, such as some mycoses; however, the origin of these diseases is clearly different:

  • Acanthosis nigricans : cutaneous manifestation characterized by hyperpigmented, not delimited areas, which typically appear at the level of skin folds. The skin appears thickened, with a velvety surface and dark brown color.
  • Candidiasis : superficial infection of the skin and mucous membranes caused by a fungus of the genus Candida . It is localized mainly between the folds of the skin and is favored by maceration. The event includes redness, blistering and exudation of the affected skin.

  • Allergic contact dermatitis : immune reaction of the skin to an allergen (for example: nickel, chromium, cobalt, dyes) which induces an inflammation process (also called topical eczema). It manifests as redness, scaling, blisters, abrasions and scabs.

  • Irritant contact allergic dermatitis : like the previous one, it is a skin inflammation caused by the intervention of irritants, accompanied by lesions and the characteristic signs of the allergic reaction, as well as a burning sensation or pain and sometimes itching.

  • Intertrigo : dermatosis produced by the reciprocal rubbing of two adjacent skin surfaces, also called intertrigo, characterized by redness and exudation (erythrasma shows no margin).

  • Psoriasis : chronic inflammatory disease of the skin that can also occur with scaly patches of thickened skin (especially the form of plaque psoriasis can be confused with erythrasma, as both lesions are scaly).

  • Seborrheic dermatitis : it affects areas rich in sebaceous glands of the skin (especially scalp, face, chest and ear canal); its appearance is characterized by yellowish and greasy scales, and is associated with erythema and folliculitis.

  • Tinea corporis : superficial mycosis that affects the skin in areas of the body devoid of hair, manifesting itself with itching and circular pinkish lesions, desquamative, with sharp edges in relief and lighter center.

  • Tinea cruris : fungal infection affecting groin and thighs. Mycosis appears as a small erythema (round spots, lighter center, well-defined margins, scaling) and annoying itching (erythrasma is not associated with an itchy sensation).

  • Tinea pedis : mycosis mainly caused by Trichophyton, located initially between the toes of the sole of the foot. This infection is manifested by itching, burning, redness, scaling, abrasion and rash.

Diagnosis

The diagnosis of Erythrasma is placed on an outpatient basis with the aid of Wood's lamp. The condition cannot be diagnosed with a blood test or blood culture, but there are specific microbiological cultures that allow Corynebacterium minutissimum to be isolated (first, however, the doctor must obtain clinical indications on the potential responsible micro-organism, in order to prepare the correct analysis).

  • Wood lamp examination: the analysis of erythrasma lesions reveals a coral red color to the fluorescence. The cause of this color has been attributed to the synthesis of coproporphyrin III in excess, by these microorganisms. Coproporphyrin accumulates in the skin tissues and, when exposed to a Wood lamp, emits a typical coral red fluorescence which allows to highlight any infection hearths. The results can be falsely negative when the patient cleanses the skin before undergoing the test (the pigment can be washed away). In case of suspicion it may be necessary to repeat the exam the next day.

Axillary erythrasma and appearance of erythema-affected skin on Wood's lamp

Source images: //www.dermnetnz.org/bacterial/erythrasma.html

In short: coproporphyrin III in human physiology

Coproporphyrin is a pigment with a tetrapyrrolic structure belonging to the porphyrin group. Coproporphyrins are contained in various human organs and are usually eliminated in small quantities via urine and intestinal tract. Coproporphyrin III is an intermediate product of hemoglobin biosynthesis.

  • Microbiological culture: to highlight an alteration in the bacterial flora it is possible to collect a sample to be subjected to microbiological examination, by scraping the lesion. The Gram stain shows long filaments that reveal the presence of Corynebacterium minutissimum: the microorganisms do not produce haemolysis (enzymes do not therefore induce the rupture of red blood cells) and grow in culture in smooth colonies of 1.5 mm.
  • Histological examination: the bacteria that cause erythrasma are present in the stratum corneum and can be seen due to the typical filamentous formations in which they are structured. Histological examination of the lesions contributes to providing diagnostic evidence.

Treatment

The goal of drug therapy is to limit bacterial proliferation, eradicate the infection and prevent complications. Gently cleaning the stains on the skin surface with bactericidal or antifungal soaps can help limit bacterial proliferation. Topical administration of erythromycin is very effective (macrolide antibiotic that inhibits protein synthesis). In severe cases, the doctor may prescribe systemic therapy.

To eradicate the infection with Corynebacterium minutissimum it is possible to use antibacterial and / or antifungal agents, which also allow to control concomitant infections. The drug of choice is erythromycin; the infection can be treated either with topical or systemic administration (oral intake).

Generally the recommended initial therapy is based on the administration of fusidic acid (bacteriostatic antibiotic, which limits bacterial replication without killing the microorganism) or, alternatively, the application of a topical tetracycline (antibiotic that acts by inhibiting protein synthesis). In the event of treatment failure, a drug with a systemic effect should be chosen, such as amoxicillin-clavulanic acid (amoxicillin belongs to the penicillin group and works in synergy with clavulanic acid, which increases the efficiency of the antibiotic blocking the activity of bacterial enzymes beta-lactamase).

Corynebacterium minutissimum and antibiotic sensitivity :

Erythrasma is usually treated with fusidic acid (topically), systemic macrolides (such as erythromycin and clarithromycin) and / or azole derivatives (antifungal agents, example: imidazole).

Corynebacterium minutissimum is generally sensitive to penicillins, first-generation cephalosporins, erythromycin, clindamycin, ciprofloxacin, tetracycline and vancomycin.

We can highlight the following degree of sensitivity for the drugs listed above:

  • Corynebacterium minutissimum is positively affected by treatment with erythromycin or erythromycin
  • the bacterium is not very sensitive to penicillins and scarcely to ciprofloxacin

Furthermore, the bacterium can develop resistance to different therapeutic agents (multi-resistant strains have been isolated and often the isolation by culture and the antibiogram are not performed).

In summary: therapeutic options for erythrasma

Topical agents

bactericidal or antifungal soaps, erythromycin (gel), fusidic acid (ointment)

Antibiotics

erythromycin, clarithromycin

Topical antifungal agents with activity for erythrasma

miconazole, clotrimazole, econazole

An alternative treatment can be provided by photodynamic therapy with red light (broad band, peak at 635 m), able to eradicate erythrasma in some cases.

Under conditions of co-infection, therapy must be systemic and targeted at pathogens involved in the clinical setting.

Complications

Following the onset of erythrasma the following complications are possible:

  • fatal septicemia in immunocompromised patients;
  • infective endocarditis in patients with valvulopathies;
  • Corynebacterium minutissimum infection in post-surgical wounds.

Prognosis

The prognosis for erythrasma is excellent and includes complete recovery following treatment. However, the condition tends to recur if the predisposing factors are not eliminated.

Prevention

The following measures may reduce the risk factors that predict erythema infection:

  • take care of hygiene on a daily basis;
  • keep the skin dry;
  • wear clean, non-occluding clothing;
  • avoid excessive heat or moisture;
  • maintain a healthy body weight.