Annular dermatoses

The term "annular dermatoses" (AD) covers a large number of clinically and aetiogenetically heterogeneous skin diseases whose easily recognizable common feature is the initially punctiform or disc-shaped, later ring-shaped morphological structure of the centrifugally expanding lesions. The diagnosis is made clinically by taking an appropriate history and analyzing the clinical aspect (acute/chronic, isolated/multiple lesions, erythema/purpura, histological substrate, etc.). Diagnostic confirmation can be provided by microscopic findings (lymphocytic, eosinophilic, neutrophilic, lichenoid).

The ability of the skin to form anular structures is referred to below as "anularity". Anularity is defined as a characteristic, multiphasic, pathological reaction of the skin. Apart from the oral mucosa, anularity is not observed on other epithelial surfaces.

Basically, anularity can be divided into:

• Primary anularity
• and
• secondary anularity.

In primary anularity , the annular pattern is an intrinsic characteristic of the respective dermatosis, irrespective of its genesis, and defines it(erythema anulare centrifugum, erythema gyratum repens, erythema chronicum migrans, granuloma anulare, etc.).

In secondary anularity, the anular patterns occur more or less randomly among their other, different clinical manifestations. Their diagnostic value is therefore limited. The list of secondary anular erythema is long.

Classification of annular dermatoses according to their clinical course

Acute anular dermatoses

• Pityriasis rosea
• Erythema anulare rheumaticum (erythema marginatum)
• Erythema marginatum with hereditary angioedema
• African trypanosomiasis
• Acute anular urticaria

Chronic annular dermatoses

• Tinea corporis
• Erythema chronicum migrans
• Anular sphilides
• Leprosy
• Erythema anulare centrifugum-like psoriasis
• Seborrheic dermatitis
• Granuloma anulare
• Granuloma faciale (granuloma eosinophilicum faciei)
• Subacute cutaneous lupus erythematosus
• Neonatal lupus erythematosus
• Neutrophilic figured erythema of infancy
• Sweet syndrome
• Erythema anulare centrifugum (Erythema annulare centrifugum)
• Varia: Familial er ythema annulare centrifugum
• Erythema gyratum repens
• Erythema gyratumperstans (Erythema anulare familiale)
• Eosinophilic annular erythema (Eosinophilic annular erythema)
• Annular lichenoid dermatitis of childhood
• Annular epidermolytic ichthyosis (OMIM:607602)

Anular purpura forms

• Purpura anularis teleangiectodes (Majocchi's purpura annularis telangiectodes)
• Anular leukocytoclastic vasculitis
• Post-infectious purpura

In primary anularity, a distinction can be made between infectious and non-infectious (idiopathic) anularity.

Infectious anularity

• Infectious primary anularity (examples: dermatophytoses, erythema chronicum migrans, pityriasis rosea) occupies a special position in that the anular pattern is defined by the growth of the pathogens (e.g. dermatophytes or borrelia). It is an expression of a defense reaction of the skin to the penetration of the pathogens. In this respect, the causality is clear.

Non-infectious anularity

• The nature of non-infectious, idiopathic, primary anularity is unknown. The prototype for this type of reaction is erythema anulare centrifugum. Parainfectious, autoimmunological, autoinflammatory, paraneoplastic or drug-induced causes are discussed. Its histological pattern is quite varied and ranges from non-specific lymphohistiocytic (example= erythema anulare centrifugum), to neutrophilic (neutrophilic figured erythema), to eosinophilic (eosinophilic anular erythema) and mixed-cell (granuloma anulare) infiltrates. And yet this type of ring formation, despite considerable diversity, is based on an unmistakable, unique reaction mechanism of the skin that leads to a similar morphological result, the anular phenotype.

In principle, the anularity of a dermatosis is not a static but always a dynamic process. The anular figures on the skin change over time, even in the short term between two consultations. In this respect, it makes sense to ask about the dynamics when taking the medical history and to document them during multiple visits.

Initially, annular erythema (AD) appears as flat, centrifugally growing, erythematous papules or plaques that develop their annularity through central fading. The confluence of neighboring, initially closed lesions leads to arcuate, open, polycyclic or band-shaped patterns. The International League of Dermatological Societies (ILDS), in its recent update of the glossary of descriptive terms for skin lesions, proposed the use of the following terms: anular, arcuate, polycyclic or oval (Nast A et al. 2016).

Careful examination of the surface of the lesion can determine whether the process originates from the epidermis (e.g. in dermatophytoses) or from the dermis (e.g. in erythema chronicum migrans). Anular purpura is easy to clarify diascopically.

The heterogeneous, pediatric, annular erythema occupies a special position in the literature (Tab). Their relationship to anular dermatoses in adults is not always clear.

According to the histologic pattern, they can be classified as follows:

• Lymphocytic annular dermatoses (erythema anulare centrifugum, erythema chronicum migrans)
• Eosinophilic anular dermatoses (eosinophilic anular erythema)
• Neutrophilic anular dermatoses (neutrophilic figured erythema of childhood)
• Mixed cellular anular dermatoses (granuloma anulare, erythema anulare centrifugum)

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