Exploring itch in hidradenitis suppurativa with lessons from atopic dermatitis and psoriasis

Itch is a prominent symptom in many cutaneous disorders, including atopic dermatitis (AD), prurigo nodularis, and psoriasis. Itch is also a common but overlooked concern in patients with hidradenitis suppurativa (HS). Currently, the mechanisms underlying itch in HS remain unclear. To gain a better understanding, we reviewed the literature on pruritus in HS and other itch-predominant disorders, AD, and psoriasis. In HS, psoriasis, and AD, we found that itch often co-localized with pain and occurred more frequently at night. Furthermore, itch was found to negatively affect sleep and increase the risk for comorbid psychiatric disorders in HS, psoriasis, and AD. However, HS-, psoriasis-, and AD-related itch differ in temporality. Itch in AD is often described as chronic, while itch in HS and psoriasis is often described as episodic. HS-associated itch is likely multifactorial, and several mechanisms have been proposed including peripheral sensitization, central sensitization, and neuroinflammation. Prior studies in HS highlight enhanced IgE production and a dense infiltration of mast cells, along with a variety of cytokines and chemokines. Furthermore, alterations in the skin microbiome may contribute to itch in HS. To date, few therapies have been studied to treat itch in HS. Given the efficacy of several biologics and small molecules in treating itch in AD and psoriasis, similar agents may be explored in future HS studies. Alternative therapies to target neurological and psychiatric contributions to itch may include anticonvulsants, cannabinoids, and nonpharmacological treatments. In conclusion, pathomechanisms of itch in HS remain to be fully elucidated. However, we can draw on lessons from other pruritic disorders to begin addressing the symptom of it and identify important questions for future study.