8.4 Itching

Pruritus. 

Prevalence: most common symptom in dermatology. Chronic itch 12-20% of general population. In particular, about 60% of the elderly complain of chronic itch. According to different dermatoses or non-dermatoses associated itch, no clear data exists.

Itching is a symptom of many dermatoses or a symptom of a specific physical or psychological sensation. It produces unpleasant feeling of the skin leading to the desire to scratch.  

Different stimuli lead to a provocation of scratching in order to remove a pruritogenic factor, a response likely to have originated when most pruritogens were parasites. Dedicated neural pathway (pruritoceptors) similar but different compared to those dedicated to pain, including unmyelinated C fibers and small myelinated Aδ fibers. Itch mediators include histamine, IL-2, TNF-a, IL-4, IL-13, IL-31, thymic stromal lymphoprotein, proteases, neuropeptides (substance P) and opioid peptides. 

Desire to scratch. Quality of itch: burning, painful, stinging, prickling. Itch may be continuous or intermittent (continuous over the day or may come up at certain times during night or may flare up by stress or when patients go to rest). 

Localized pruritus: usually caused by itchy dermatoses, associated with inflamed skin. Generalized pruritus: can be caused by itchy dermatoses even if the inflamed skin does not show generalized spread, or can be caused by extracutaneous disorders or underlying systemic disorders. 

- Acute;
- Chronic: Itching lasting 6 or more weeks. Localized or generalized.

• Pruritus with underlying dermatosis (specific skin lesions): atopic dermatitis, eczema, psoriasis, urticaria, scabies, pemphigoid, drug eruptions, cutaneous T cell lymphoma, insect bite reactions.
• Pruritus associated with excoriated nodules and/or lichenification: prurigo nodularis, lichen simplex chronicus.
• Pruritus in patients with normal skin or minimal scratched lesions (pruritus of unknown origin): neurological diseases, hematological disorders, endocrine diseases, infective diseases, uremic, cholestatic, metabolic diseases, neoplastic, drug-induced, psychiatric diseases, mixed.

Recommended in patients with pruritus of unknown origin certain blood parameters and imaging techniques as well as biopsy.

It depends on the type of skin lesions present. In chronic itch an increase of nerve fibres in the upper dermis also reaching epidermis can be found.

The course is depending on the underlying disease and may last months or decades. Itch negatively impacts on the quality of life. Severe itch may be devastating. 

Secondary skin lesions caused by scratching. Usually, secondary skin lesions encompass excoriations, ulcerations, crusts, papules, nodules, lichenification, atrophy and scars, hyper- and hypopigmentation. Sleeping disorder. Suicidal ideation. 

In depth case history, physical examination of skin and lymph nodes, assessment of itch severity, screening lab and instrumental tests. 

Differentiate pruritus from burning sensations (porphyrias). Specific polyneuropathies. 

Relaxation, mental training, yoga, mindfulness, avoidance of scratching training.

Prevention of dry skin with emollients.

Symptomatic therapy and treatment of underlying disease (where present). Topical treatments: local anaesthetics, topical corticosteroids, topical calcineurin inhibitors. Systemic treatments: antihistamines, short term corticosteroids, ciclosporin. Opioid receptor agonists and antagonists, antiepileptics. Antidepressants, neurokinin antagonists, biologics. Ultraviolet phototherapy.