Diseases associated with hidranitis suppurativa: part 2 of a series on hidradenitis.

Hidradenitis suppurativa (HS), a pathologic follicular disease, impacts patients' lives profoundly and usually occurs in isolation. The diseases with the strongest association are obesity, depression, and pain. HS is associated with many diseases including acne conglobata (AC), dissecting cellulitis, pilonidal cysts, and obesity. Pyoderma fistulans sinifica (fox den disease) appears to be the same entity as Hurley Stage 2 of 3 HS. The rate of acne vulgaris in HS patients mirrors unaffected controls. The most common, albeit still uncommon, association is with seronegative, haplotype unlinked arthritis (most importantly B27), in particular spondolyarthritis. Crohn disease and HS occur together at a rate that varies from 0.6% to 38% in retrospective cases series. Ulcerative colitis occurred with HS in 14% of patients in one series. The next most common association is with pyoderma gangrenosum, but this association is likely under-reported. Synovitis-Acne-Pustulosis Hyperostosis-Osteitis (SAPHO) syndrome, which is rare, has more than 10 reports linking it to HS. Nine case reports have linked Dowling-Degos disease (DDD) to HS and two reports related HS to Fox-Fordyce disease (FF), but because both occur in the axilla this might be a mere coincidence. HS is rarely associated with ophthalmic pathology. Specifically, more than 5 reports link it to Keratitis-Ichthyosis-Deafness syndrome (KID); greater than10 cases link it to interstitial keratitis and 2 cases are linked to Behçet's disease. The presence of proteinuria and acute nephritis link HS to the kidney, especially since and reports have documented resolution of HS after renal transplant. Florid steatocystoma multiplex, Sjogren Syndrome, and HS have been linked and their reports likely underestimate their coincidence because all these entities involve occlusion (albeit by different mechanisms). Three reports link HS and amyloid, but both share some common genetic underpinnings and thus the coincidence of these diseases is likely underreported. Pyoderma vegetans has been noted in 2 cases of HS and 4 cases of Inflammatory Bowel Disease (IBD) and is likely a clue to the linkage of the pathology of IBD and HS. Pityriasis rubra pilaris, in particular Type VI related to HIV, has a relationship more commonly with acne conglobata, but with HS also. Single case reports of diseases associated with HS include systemic lupus erythematosus, acromegaly, Down syndrome, Bazex-Dupre´-Christol, and prurtis ani, but these might be coincidences. Pyogenic Arthritis, Pyoderma gangrenosum, and Acne (PAPA Syndrome) and Pyoderma gangrenosum, Acne, and Suppurative Hidradenitis (PASH Syndrome) are pyodermic-arthritic syndromes that are associated with HS. Erythema nodosum and granulomatous lobular mastitis have been reported with HS but the significance of these reports is uncertain. Because of scarring, HS can result in lymphedema including scrotal elephantiasis and verrucous lymphedema. HS is sometimes accompanied by obesity, hypertension, and anemia and can be considered a disease in the spectrum of metabolic syndrome, a skin disease with systemic consequences. HS, like other types of chronic inflammation when long standing in the perianal and perineal areas, can result in squamous cell cancer. A variety of drugs can induce HS. These include lithium, sirolimus, cyclosporine, vemurafenib, and oral contraceptives. Inverse psoriasis or psoriasis vulgaris as a side effect of infliximab therapy may be associated with HS. These associations aside, most cases of HS occur in isolation without coincident morbidity.