Improving the Differential Diagnosis of Hidradenitis Suppurativa
Hidradenitis suppurativa (HS) is a chronic, painfully debilitating skin condition. The common signs and symptoms include blackheads, often appearing in pairs and small pitted areas of skin; large painful abscesses that can break open to leak foul-smelling pus; and painful pea-size lumps under the skin that can persist for weeks or months and are often seen in areas such as the armpits, groin, buttocks, and breasts.1 Over time, tunnels form under the skin connecting the lumps and may drain blood and pus.
Despite its severe impact on quality of life, HS is plagued by a delay in accurate diagnosis, estimated globally at more than 7 years.2 Longer diagnostic delays of a decade or more have been reported in some studies.3 Delayed diagnosis is among the several unmet needs cited by patients and health care professionals related to managing HS.4 Multiple factors contribute to diagnostic delays, including under-recognition by doctors, embarrassment and stigma associated with the disease, and socioeconomic barriers.2 The psychological impact of HS can be devastating. An active HS lesion is associated with persistent pain, body odor, and physical disfigurement. Patients often experience embarrassment, low self-esteem, anxiety, depression, disabling social stigma, and a reluctance to develop interpersonal relationships.5
The exact prevalence of HS is unknown, although globally it has been estimated to range from 0.1% to 4% of the general population; the wide variation in prevalence is likely related to the differences in the included population who may or may not have diagnostic confirmation of HS and the differences in methodologies, including the use of validated and nonvalidated screening questionnaires.2 Crude age-specific prevalence estimates for HS in the United States are available in Figure 1.6
In general, HS is diagnosed by dermatologists; however, patients often consult several physicians for years before receiving a correct diagnosis.3 These physicians commonly include general practitioners, surgeons, and gynecologists, who may need to make the appropriate referral to a dermatologist, increasing the probability of diagnostic delays and misdiagnosis. The most common misdiagnoses include abscess, ingrown hair, and folliculitis. Disease progression and severity continue during diagnostic delay with ongoing tissue destruction and increased sites requiring surgical treatment. Strategies are needed to minimize diagnostic delays or misdiagnosis. Accurate, prompt diagnosis and staging of disease severity are essential for optimal evidence-based treatment.
Diagnostic Approach and Criteria
The diagnosis of HS is clinical. A full-body skin examination is required to assess the extent and severity of HS and determine the treatment’s impact. Due to the diagnostic requirement for recurrence and chronicity, an observation period may be necessary before the definitive diagnosis is made. A definitive diagnosis requires all 3 of the following criteria to be present 7:
- Typical deep-seated painful nodules, often described as “blind boils,” must be present. Other lesions are abscesses, inflamed tunnels, bridged scars, and postinflammatory “tombstone” double-ended pseudocomedones. These nodules must not be confused with conditions such as superficial folliculitis;
- The nodules occur in ≥1 area of the body typically affected by HS, including the armpit, groin, perineal region, buttocks, and inframammary and intermammary folds; and
- There must be a clear history of chronicity and recurrence. In general, 2 recurrences over 6 months have been used as a qualifier for a diagnosis.
Clinical examination alone, however, may underestimate the severity and disease involvement of HS. Patients often describe the pain associated with HS as hot, burning, pressure, cutting, sharp, taut, splitting, gnawing, sore, throbbing, and aching. Other diagnostic factors may include prodromal symptoms such as local erythema, paresthesia, and pruritus as well as systemic symptoms such as malaise, headache, and nausea. Patients with prodromal symptoms reported that these symptoms preceded their flares about 90% of the time.8
Previously considered of limited value, laboratory investigations have their place in diagnostic evaluations. Bacterial cultures from samples taken from the lesions can detect resistant organisms. Patients with acute lesions may have elevated white blood cell count and erythrocyte sedimentation rate (ESR). Therefore, appropriate laboratory investigations include complete blood cell count with differential and platelet counts, ESR, C-reactive protein (CRP), urinalysis, serum iron level, and serum protein electrophoresis. Indeed, blood biomarkers have been used to assess deep-seated inflammatory processes that cannot be seen near the skin surface. The increased expression of several inflammatory proteins correlates with the extent of inflammatory skin alterations in patients with HS. These include tumor necrosis factor, ESR, CRP, serum interleukin-6 (IL-6), and chitinase-3-like protein 1 (YKL-40).5 However, skin biopsy is not recommended due to the nonspecific nature of the histopathology.
Role of Imaging in HS Diagnosis
Imaging can play an important role in diagnostic evaluations. Magnetic resonance imaging can potentially help preoperative assessment of fistulation in the anogenital area to exclude the occurrence of fistulas that communicate with the rectum or anal canal. Imaging studies with ultrasound have revealed diffuse alteration of dermal echogenicity patterns, dermal thickening and pseudocysts, widening of hair follicles, identification of fluid collections, and fistulous tracts that were not detected clinically. In a study of 142 lesional areas in 34 HS patients, ultrasound evaluation resulted in management modification of 82% of the HS patients; 24% of the cases changed from medical to surgical management.9
Other Supporting Criteria for Diagnostic Evaluation
Patient-reported outcome measures have also been used in diagnostic evaluations. Commonly used measures include the Dermatology Life Quality Index (DLQI) to assess the impact of skin disease and the Visual Analogue Scale (VAS) or Numeric Rating Scale (a segmented numerical version of the VAS) to assess pain and itch. The DLQI is also helpful for the assessment of HS on daily life.10 Less commonly used outcome measures are the Hidradenitis Suppurativa Global Assessment Scale, the Hospital Anxiety and Depression Scale, the Work Ability Index, and Work Productivity and Activity Impairment.
Suspicion of the diagnosis can also be strengthened by other factors that are not pathognomonic. Nonpathognomonic factors that can be used to support an HS diagnosis include7:
- Family history of HS;
- Recurrent inflammatory noncharacteristic lesions in a location typical of HS;
- Lesions typical of HS in unusual locations (often pressure points and areas experiencing enhanced mechanical friction); and
- Presence or history of pilonidal sinus.
Overall, it is important not to rule out a diagnosis of HS too quickly. It is also essential to consider other conditions with a similar clinical presentation before diagnosing patients with HS, keeping in mind that some conditions may be comorbidities of HS.
Distinguishing HS From HS Mimics
The differential diagnosis of HS can be challenging and complex due to overlapping clinical presentations. Common mimics include bacterial and fungal infections, cysts, and cutaneous Crohn disease; indeed, the close clinical presentations between HS and the cutaneous manifestations of Crohn disease, a chronic inflammatory gastrointestinal disorder, can result in misdiagnosis.11 In a study of 1093 patients with inflammatory bowel disease, the prevalence of HS was found to be 23%.12
Differential diagnosis is also challenged by the nonspecificity of histopathology, requiring several diagnostic approaches. Consequently, missing HS or misdiagnosis is common. Common mimics and their differentiation from HS are summarized in Table 1.13
Once a diagnosis of HS has been made, it is essential to classify the disease severity to tailor treatment. Several disease severity scoring systems have been developed; currently, there is no gold standard scoring tool because each has both advantages and limitations in daily practice, and not all are validated for clinical use (Table 2).7,11,14,15,16
The Hurley scoring system is the most commonly used HS classification in the clinical and research settings (Table 3).16 While it is reasonable to use the Hurley staging to guide treatment decisions, it is important to recognize that each stage may have wide variability of disease presentation. Therefore, it has been suggested that the MSS be used to measure the efficacy of treatments because of its higher precision.8
Hidradenitis suppurativa is a chronic, painfully debilitating skin condition with a significant negative impact on quality of life. Diagnostic delays and misdiagnosis result in disease progression and increasing complications.
The differential diagnosis of HS is clinical in approach, requiring specific criteria to be met and ruling out diseases that can mimic the condition. Supporting diagnostic evaluations include prodromal symptoms, nonpathognomonic factors, and laboratory investigations, including complete blood cell count and inflammatory proteins such as ESR, CRP, and IL-6. Magnetic resonance imaging has also been used to support diagnostic evaluation. Accurately staging HS according to severity is vital to tailoring treatments to meet patients’ specific needs. Several disease severity scoring systems are available, each with advantages and disadvantages. Currently, the Hurley scoring system is the most commonly used HS classification in clinical and research settings.
1. Hidradenitis suppurativa: signs and symptoms. American Academy of Dermatology. Updated May 5, 2022. Accessed December 9, 2022. https://www.aad.org/public/diseases/a-z/hidradenitis-suppurativa-symptoms
2. Kearney N, Kirby B. The prevalence of hidradenitis suppurativa outside the hospital setting: the impact of the undiagnosed. Br J Dermatol. 2022;186(5):767-768. doi:10.1111/bjd.21293
3. Kokolakis G, Wolk K, Schneider-Burrus S, et al. Delayed diagnosis of hidradenitis suppurativa and its effect on patients and healthcare system. Dermatology. 2020;236(5):421-430. doi:10.1159/000508787
4. Willems D, Hiligsmann M, van der Zee HH, Sayed CJ, Evers SMAA. Identifying unmet care needs and important treatment attributes in the management of hidradenitis suppurativa: a qualitative interview study. Patient. 2022;15(2):207-218. doi:10.1007/s40271-021-00539-7
5. Wang SC, Wang SC, Sibbald RG, Alhusayen R, Bashash M, Alavi A. Hidradenitis suppurativa: a frequently missed diagnosis, part 1: a review of pathogenesis, associations, and clinical features. Adv Skin Wound Care. 2015;28(7):325-332. doi:10.1097/01.ASW.0000465674.34810.e9
6. Garg A, Kirby JS, Lavian J, Lin G, Strunk A. Sex- and age-adjusted population analysis of prevalence estimates for hidradenitis suppurativa in the United States. JAMA Dermatol. 2017;153(8):760-764. doi:10.1001/jamadermatol.2017.0201
7. van der Zee HH, Jemec GB. New insights into the diagnosis of hidradenitis suppurativa: Clinical presentations and phenotypes. J Am Acad Dermatol. 2015;73(5 Suppl 1): S23-S26. doi:10.1016/j.jaad.2015.07.047
8. Duran C, Baumeister A. Recognition, diagnosis, and treatment of hidradenitis suppurativa. JAAPA. 2019;32(10):36-42. doi:10.1097/01.JAA.0000578768.62051.13
9. Wortsman X, Moreno C, Soto R, Arellano J, Pezo C, Wortsman J. Ultrasound in-depth characterization and staging of hidradenitis suppurativa. Dermatol Surg. 2013;39(12):1835-42. doi:10.1111/dsu.12329
10. Pinard J, Vleugels RA, Joyce C, Merola JF, Patel M. Hidradenitis suppurativa burden of disease tool: pilot testing of a disease-specific quality of life questionnaire. J Am Acad Dermatol. 2018;78(1):215-217.e2. doi:10.1016/j.jaad.2017.08.030
11. Sabat R, Jemec GBE, Matusiak L, et al. Hidradenitis suppurativa. Nat Rev Dis Primers. 2020;6(1):18. doi:10.1038/s41572-020-0149-1
12. van der Zee HH, de Winter K, van der Woude CJ, Prens EP. The prevalence of hidradenitis suppurativa in 1093 patients with inflammatory bowel disease. Br J Dermatol. 2014;171(3):673-5. doi:10.1111/bjd.13002
13. Saunte DML, Jemec GBE. Hidradenitis suppurativa: advances in diagnosis and treatment. JAMA. 2017;318(20):2019-2032. doi:10.1001/jama.2017.16691
14. Napolitano M, Megna M, Timoshchuk EA, et al. Hidradenitis suppurativa: from pathogenesis to diagnosis and treatment. Clin Cosmet Investig Dermatol. 2017;10:105-115. doi:10.2147/CCID.S111019
15. Scuderi N, Monfrecola A, Dessy LA, Fabbrocini G, Megna M, Monfrecola G. Medical and surgical treatment of hidradenitis suppurativa: a review. Skin Appendage Disord. 2017;3(2):95-110. doi:10.1159/000462979
16. Shaver RL, Jemec GBE, Freese R, Alavi A, Lowes MA, Goldfarb N. A survey of clinicians regarding preferred severity assessment tools for hidradenitis suppurativa. Int J Dermatol. 2021;60(6):e248-e251. doi:10.1111/ijd.15295
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Reviewed January 2023