Follicular occlusion tetrad

Abstract

Follicular occlusion tetrad is a symptom complex consisting of four conditions having a similar pathophysiology. It includes Hidradenitis suppurativa, acne conglobata, dissecting cellulitis of the scalp and pilonidal sinus. The exact pathogenesis of this group of disease is unknown but evidence suggests that they share the same pathological process initiated by follicular occlusion in apocrine gland bearing areas. Though each of these conditions is commonly encountered singly, follicular occlusion tetrad as a symptom complex has been rarely reported in the literature.

Sonographic Comparison of Morphologic Characteristics Between Pilonidal Cysts and Hidradenitis Suppurativa

“…Instead, the plugging of the hair follicles would be a secondary event generated as a consequence of deregulation of the signaling mechanisms and processes in charge of the development and functioning of the hair, which include the abnormal differentiation of stem cells, the ectopic production of keratin and hair tract fragments, as well as anomalous healing and inflammatory processes. The same processes may also be unregulated in other related diseases reported as part of the follicular tetrad, such as dissecting cellulitis of the scalp and acne conglobate . Nevertheless, further research on the sonographic link between these entities may be needed.…”

“…Pilonidal cysts and hidradenitis suppurativa are related inflammatory conditions that have been included in what is called the “follicular occlusion tetrad” that draw together 4 pathologic conditions that seem to share plugging of the hair follicles in their physiopathologic mechanisms. The remaining 2 entities of the tetrad are acne conglobate and dissecting cellulitis of the scalp . Thus, both hidradenitis suppurativa and pilonidal cysts are commonly present in corporal regions with cutaneous folds that may be subject to high levels of mechanical stress, something that has been proposed as a potential trigger of hidradenitis suppurativa …”

“…Since both pilonidal cysts and hidradenitis suppurativa present with alterations of the hair, knowledge of the normal sonographic morphologic characteristics of the hair follicles and tracts, which already have been reported in the literature, might be relevant for a better understanding of the alterations in the diseases that constitute the follicular occlusion tetrad, such as pilonidal cysts and hidradenitis suppurativa …”

Hidradenitis suppurativa: from pathogenesis to diagnosis and treatment

“…An association between rheumatologic joint conditions, namely spondyloarthropathies, and synovitis, arthritis, pustulosis, hyperostosis, osteitis syndrome has also been seen in conjunction with HS 70,76. Moreover, due to common shared etiopathogenetic factors such as follicular occlusion from infundibular hyperkeratosis and follicular epithelium hyperplasia, HS has also been possibly reported in conjunction with other follicular occlusion disorders like acne conglobata, dissecting cellulitis of the scalp, and sinus pilonidalis,70 creating the follicular occlusion tetrad: HS, acne conglobata, dissecting cellulitis, and pilonidal cysts 78. Finally, as regards HS-related malignancies risk, squamous cell carcinoma (SCC) has been reported to possibly arise within or neighboring HS lesions (from 1% to 3.1% of evaluated HS patients) 79.…”

Update on Hidradenitis Suppurativa (Part I): Epidemiology, Pathogenesis, Severity assessment and Comorbidities

“…1,18 In addition, HS belongs to the group of diseases characterized by follicular occlusion known as the follicular occlusion tetrad: HS, acne conglobata, dissecting cellulitis of the scalp, and pilonidal cysts. 64 Acne vulgaris, keratitis-ichthyosis-deafness syndrome and Dowling-Degos disease have also been associated with HS. 1,18 Scarce data also proposed a link between HS and Down syndrome.…”