Hidradenitis suppurativa, also known as acne inversa, is an inflammatory skin disease of unknown cause. It has an autosomal dominant inheritance pattern, and androgen excess has been postulated 7. The disease is associated with Crohn disease and Dowling Degos disease.
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Epidemiology
Up to 4% of the general population is affected to some degree by hidradenitis suppurativa (see Hurley stages below). There is a significant female preponderance.
Risk factors
Clinical presentation
Hidradenitis suppurativa is characterized by recurrent abscesses, sinus tracts and scarring in regions of predisposition. The disease affects areas bearing apocrine or sebaceous glands: groin, buttocks, inner thighs, axillae, and inframammary regions.
Anogenital disease may tract deeply into muscle, fascia and bowel potentially leading to a "labyrinth" of disease in advanced cases 7. Notably, perianal disease specifically may mimic other common conditions such as anal fistula, pilondial disease, perianal abscess or Crohn disease 7.
Clinical staging
Hidradenitis suppurativa is classifed clinically into three stages in the Hurley staging system 1:
stage 1: solitary or multiple isolated abscess formation; no scarring or sinus tracts; resembling acne vulgaris
stage 2: recurrent abscesses, single or multiple widely separated lesions; sinus tract formation is present; this can restrict movement and incision and drainage may be required
stage 3: diffuse or broad involvement across a regional area with multiple interconnected sinus tracts and abscesses; fistulisation and scarring
Pathology
Based on histological features, it is considered inflammatory and originating from the hair follicle; hence, the term 'acne inversa' is favored by some experts. The exact etiology is uncertain.
Radiographic features
The diagnosis of hidradenitis suppurativa is clinical, and imaging is non-specific.
Ultrasound
A number of features can be identified by ultrasound. These features include both actual lesions and possible predisposing factors such as skin thickness and hair follicle morphology 5.
MRI
MRI is the test of choice to assess the extent and for complications. MRI is also useful to differentiate from Crohn disease 2, the main differential diagnosis.
STIR is considered the most useful sequence.
marked thickening of the skin
induration of the subcutaneous tissues
formation of multiple subcutaneous abscesses
sinus and fistula formation remote from anorectal region (cf. Crohn disease) 3
PET
Focal intense FDG uptake in affected areas has been reported 4.
Treatment and prognosis
Management with antibiotics and other non-surgical interventions such as retinoids and corticosteroids may relieve early symptoms. Severe cases may be treated with immunosupressive agents 7.
Radical surgery (e.g. radical excision of all apocrine-bearing tissue) may be necessary for control and to prevent recurrence. Excision of affected skin however, is complicated by a recurrence rate of over 50% 7.
The condition has a significant impact on quality of life 7,11.
Differential diagnosis
The differential diagnosis for hidradenitis suppurativa includes: