1.5.6 Prurigo Simplex

Prurigo simplex subacuta. Prurigo ferox, prurigo Hebra, prurigo nodularis Hyde, prurigo mitis, and prurigo Besnier. Itchy Red Bump disease.

Rather common disease in aged individuals. Prevalence estimate of 0.19% for patients aged 18 to 64 years in the United States and a prevalence of 0.21% in Germany in 2010 Woman 20-30 years , male > 60 years.

Group range of pruritic, papulous conditions lacking clear diagnostic criteria, all featuring intense pruritus followed by reactive crusted papules (prurigo = itchy crust). Chronic prurigo (CPG) today is defined as a neuroinflammatory, fibrotic dermatosis with presence of chronic pruritus (itch lasting longer than 6 weeks), scratch-associated pruriginous skin lesions and history of repeated scratching.

Controversial discussion on pruritic papular eruption. No common sense if prurigo simplex or “itchy red bump” disease is a clearly defined entity or a variant of chronic prurigo. It has been suggested that it is a transitional stage of prurigo that transforms from an acute to a chronic form. Prurigo seems to develop in individuals, who overreact to an existing pruritus (itching). Causes: systemic triggers of pruritus, idiopathic. Immunologic components with IL-4 and IL-31 overexpression discussed. Most commonly observed internal disease was diabetes but hypertension and renal disease are also mentioned.

Neuroimmunological and psychosomatic interactions are important .

Pruritus, papules, papulo-vesicles and excoriations with symmetrical distribution on the extensor surfaces of the extremities, neck, lower trunk, and buttocks. Middle-aged patients, especially women, are affected. Typically, patients present with widespread dome shaped papules, sometimes in a symmetrical distribution, which are intensely itchy.

Acute, subacute and chronic forms with intense itch.

CPG:

• chronic papular prurigo (< 1 cm in diameter)

• chronic nodular prurigo (l >1 cm in diameter)

• chronic plaque prurigo

• chronic umbilicated prurigo

• chronic linear prurigo

The intensity of itch and the underlying causes of CPG do not differ between the various subtypes, which means that the clinical subtypes seem to belong to a common spectrum of one disease group

Serum: glucose, HLA1C (diabetes mellitus in 25%), liver and kidney markers, IgE and when indicated specific IgE’s, ECP (DD: prurigo type of atopic dermatitis), epidermal transglutaminase (DD: dermatitis herpetiformis, rarely).

Blood: Eosinophils (DD: prurigo type of atopic dermatitis), differential blood examination, BSR (DD: haematological disorders, rarely).

PRICK-Test (54% positive).

Psychological/psychiatric examination (67% abnormal).

Intraepidermal sero-hemorrhagic vesicle with or without crust, infiltration of lymphocytes, with a few histiocytes and scattered eosinophils in the papillary dermis Proliferation of subepidermal nerve fibres that penetrate epidermis in the healing phase (pruritic).

Superinfections of excoriated lesions, sleep deprivation. Development of nodules and nodes.

• Atopic dermatitis (prurigo variant, late age form).

• Dermatitis herpetiformis and

• Bullous pemphigoid (prurigo variant).

• Acquired reactive perforating dermatoses.

Secondary prevention: Exclude underlying disorders and avoid scratching.

Therapy:

• Topical: corticosteroids, capsaicin cream, phototherapy.

• Systemic: antihistamines.

• Anti-IL31 receptor monoclonal antibodies (nemolizumab), dupilimumab, abrocitinib baricitinib (selective JAK1-and JAK2-inhibitor) and topical ruxolitinib crèmeopioid modulator nalbuphine.