Itching for an answer: A review of potential mechanisms of scalp itch in psoriasis

Abstract

Scalp psoriatic itch is a common complaint and often poses a therapeutic challenge. The pathophysiology of this phenomenon is unclear. The unique anatomy of the scalp contains richly innervated hair follicles, abundant vasculature and perifollicular inflammatory cytokines which may all contribute to this common sensory complaint. The mast cell, in particular, is portrayed as one of the main itch conductors for its ability to trigger neurogenic inflammation, activate the peripheral hypothalamic‐pituitary‐adrenal‐axis, process and integrate itch signalling through its interactions with the scalp hair follicles. Herein, we explain and speculate upon potential mechanisms underlying itchy scalp psoriasis, involving interconnections between the neuroimmune, neurovascular and neuroendocrine systems. Many factors may play roles in itchy scalp psoriasis including the scalp hair structure, immune system, endocrine system, nervous system and vascular system. These may warrant further exploration as therapeutic targets that go beyond the application of mere anti‐inflammatory agents.

Characteristics of Pruritus according to Morphological Phenotype of Psoriasis and Association with Neuropeptides and Interleukin-31

“…Since intraepidermal sensory nerve fibers penetrate nearly the full thickness of the epidermis, such barrier defects would be expected to lower the itch threshold of sensory afferent nerve fibers 27 . Cathepsin S is overproduced by keratinocytes in patients with psoriasis relative to healthy controls 28 .…”

Fixed‐dose combination calcipotriol/betamethasone dipropionate foam provides a rapid onset of action, effective itch relief and improves patient quality of life

“…Cal/BD foam has demonstrated effective itch relief and improved itch‐related sleep loss 28 . Although its antipruritic method of action is not fully understood, 5 it appears the topical combination of vitamin D and steroid improves barrier function and may attenuate immune function by inhibiting the cascade of key ‘itch cytokines’ noted above 5,29,30 . Previous studies have demonstrated that Cal/BD foam provides effective itch relief in the overall psoriasis patient population 28 .…”

The Skin Microbiota and Itch: Is There a Link?

“…MCs recognize pathogens via pathogen-associated molecular pattern (PAMP) receptors (i.e., TLR) on their surface [66]. Once they detect pathogens, inflammatory mediators are released to attract other immune cells [67,68].…”