Spondyloarthritis and Acne Inversa: The Underdiagnosed Joint Involvement

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Language: en
Category: Treatments
Published: 2026-05-21
Last updated: 2026-05-21
Author: Dr. rer. nat. Dennis Alexander Kwiatkowski (Biochemist, Scientific Writer and Pharma Expert)
Tags: Acne Inversa, Hidradenitis Suppurativa, HS, Treatments, spondyloarthritis, axial SpA, ankylosing spondylitis, psoriatic arthritis, SAPHO, PASS syndrome, comorbidities
Joint involvement in HS is often missed despite being present in a substantial subset of patients. This article covers axial spondyloarthritis, SAPHO syndrome, PASS, and when back pain in an HS patient deserves rheumatology referral.

Medical disclaimer: This website is for general educational information only and does not replace medical advice, diagnosis, or treatment. Please speak with qualified medical professionals about symptoms or treatment decisions.

Article

The connection between hidradenitis suppurativa (HS) and spondyloarthritis is one of the comorbidity relationships in HS that is best supported mechanistically and worst recognized clinically. Spondyloarthritis — a family of inflammatory joint diseases including axial spondyloarthritis, ankylosing spondylitis, and psoriatic arthritis — occurs in HS patients at rates substantially above the general population. The IL-17 inflammatory pathway central to HS is also central to spondyloarthritis, providing a clear biological link. Yet most HS patients with joint symptoms are not assessed for spondyloarthritis, and treatment that could address both conditions is often not considered.

This article covers what spondyloarthritis is, what is known about its prevalence in HS, the specific syndromes that link HS to musculoskeletal inflammation (including SAPHO syndrome and the PASS pattern), the symptoms that warrant rheumatology evaluation, and the treatment implications when both conditions are present.
Educational content only. Diagnosis and management of spondyloarthritis requires rheumatological evaluation. This article describes general principles, not personal recommendations.

Key takeaways

- Spondyloarthritis prevalence in HS populations is reported from 1.5% to 40% in different studies, compared to <2% in the general population. The wide range reflects different study designs, patient populations, and diagnostic criteria.
- Axial spondyloarthritis (involving the spine and sacroiliac joints) is the most common form in HS; peripheral and enthesitis-related forms also occur.
- Specific clinical syndromes link HS to musculoskeletal inflammation, including SAPHO (Synovitis, Acne, Pustulosis, Hyperostosis, Osteitis) and the PASS pattern (Pyoderma gangrenosum, Acne, Suppurative hidradenitis, Spondyloarthritis).
- IL-17 inhibitors (secukinumab, bimekizumab) approved for HS are also approved for spondyloarthritis. TNF inhibitors are approved for both. The treatment overlap means a single biologic can address both conditions in a patient who has both.
- The clinical features that should prompt rheumatology assessment in an HS patient include inflammatory back pain, morning stiffness lasting more than 30 minutes, joint pain or swelling beyond what mechanical causes explain, and family history of axial spondyloarthritis or psoriasis.

What spondyloarthritis actually is

Spondyloarthritis (SpA) is a family of inflammatory rheumatic diseases sharing certain clinical and biological features. The conditions in the family include:

- Axial spondyloarthritis (axSpA) — characterized by inflammation of the spine and sacroiliac joints. Includes ankylosing spondylitis (the historical name for radiographic axSpA, when changes are visible on plain X-ray) and non-radiographic axSpA (where MRI shows inflammation before X-ray changes appear).
- Psoriatic arthritis — inflammatory arthritis associated with psoriasis (or sometimes preceding psoriasis). Can affect peripheral joints, enthesises (where tendons attach to bone), or the axial skeleton.
- Peripheral spondyloarthritis — affecting peripheral joints with characteristic SpA features (oligoarticular pattern, enthesitis, dactylitis).
- Reactive arthritis — joint inflammation following certain infections.
- IBD-associated arthritis — joint inflammation in patients with inflammatory bowel disease.

The shared features across spondyloarthritis types include: association with HLA-B27 antigen (varying by subtype), enthesitis (inflammation at tendon-bone attachments), dactylitis (sausage-like swelling of fingers or toes), inflammatory rather than mechanical pattern of joint pain, response to NSAIDs and anti-TNF therapy, and association with extra-articular features including inflammatory bowel disease, uveitis, and certain skin conditions including HS.

In the HS context, axial spondyloarthritis is the most commonly reported form, with sacroiliitis and inflammatory back pain as the typical presentation.

What the evidence shows in HS

The prevalence of spondyloarthritis in HS is variably reported, reflecting the difficulty of diagnosing spondyloarthritis (which requires combination of clinical features and imaging or laboratory criteria) and the heterogeneity of HS populations studied.

Reported prevalence ranges. Studies report SpA prevalence in HS populations from approximately 1.5% to 40%, with most reasonable estimates clustering around 3% to 8%. The lower estimates come from population-based studies; the higher estimates from tertiary referral HS centres where patients are systematically screened by rheumatologists for joint symptoms.

General population comparison. Spondyloarthritis prevalence in general populations is approximately 0.5% to 2% depending on definitions, geography, and ethnic background. Even the lower HS estimates therefore represent at least 2- to 3-fold elevation; the higher estimates reflect a substantially elevated burden in HS-dedicated cohorts.

The Schneider-Burrus cohort. A frequently cited study reported that screening HS patients with specific spondyloarthritis questionnaires identified previously undiagnosed inflammatory joint disease in a substantial fraction of HS patients — suggesting that the diagnostic gap, rather than absence of disease, accounts for much of the underrecognition in routine care.

The 2021 evidence-based screening recommendations from the US and Canadian Hidradenitis Suppurativa Foundations explicitly include spondyloarthritis among comorbidities for which screening is recommended in HS patients.

Shared biology. The IL-17 inflammatory pathway is central to both HS and spondyloarthritis. Both conditions respond to anti-IL-17 therapy (secukinumab, bimekizumab) and to TNF inhibitors. HLA-B27 — the strongest genetic risk factor for axial spondyloarthritis — has not shown strong association with HS overall, suggesting that the shared pathway operates downstream of the genetic susceptibility rather than involving identical genetic causes.

The specific syndromes worth knowing about

Several named syndromes link HS to musculoskeletal inflammation and reflect the broader inflammatory connection.

SAPHO syndrome

SAPHO (Synovitis, Acne, Pustulosis, Hyperostosis, Osteitis) is a rare inflammatory syndrome combining sterile bone and joint inflammation with neutrophilic skin disease. The skin component most commonly includes severe acne (acne conglobata, acne fulminans), palmoplantar pustulosis, or — in some patients — HS.

Clinical features:

- Sterile osteomyelitis or osteitis, often involving the anterior chest wall (sternoclavicular joints, manubrium, sternum), spine, or pelvis
- Painful bone lesions on imaging without infectious cause
- Sometimes accompanied by arthritis or enthesitis
- Severe neutrophilic skin involvement

Treatment typically involves NSAIDs, bisphosphonates for bone involvement, methotrexate, and biological therapy including TNF inhibitors and IL-17 inhibitors. Response varies, and SAPHO can be a chronic relapsing condition requiring long-term management.

Recognition in HS: patients with HS who develop chronic bone pain, particularly in the anterior chest wall or vertebral spine, should be considered for SAPHO evaluation. Imaging (MRI of suspected sites) is the principal diagnostic tool.

PASS syndrome (and related autoinflammatory clusters)

PASS — Pyoderma gangrenosum, Acne, Suppurative hidradenitis, Spondyloarthritis — describes a syndrome where these conditions co-occur in the same patient. It is grouped with related autoinflammatory clusters including PAPA (Pyogenic arthritis, Pyoderma gangrenosum, Acne) and PASH (Pyoderma gangrenosum, Acne, Suppurative hidradenitis).

These syndromes share underlying inflammasome dysregulation and neutrophilic inflammation. They are uncommon but well documented and provide a framework for thinking about how HS sits within a broader spectrum of neutrophilic and inflammatory diseases.

Clinical implication: A patient with HS who develops pyoderma gangrenosum (a separate distinctive skin condition with rapidly progressive ulcerating lesions), or severe nodulocystic acne, plus joint symptoms, should be considered for evaluation in this framework. Treatment typically involves systemic immunosuppression and biological therapy.

Hidradenitis suppurativa with axial spondyloarthritis (without specific syndrome label)

Most patients with HS plus inflammatory joint disease do not have a specific named syndrome. They have HS plus axial spondyloarthritis (or peripheral SpA) as comorbid conditions, sharing inflammatory pathways but not constituting a distinct disease entity.

This is the most common pattern. The clinical implication is straightforward: HS patients with persistent inflammatory back pain, peripheral joint symptoms, or enthesitis should be evaluated for SpA by rheumatology.

Recognizing inflammatory back pain

The most important clinical recognition skill for HS patients with potential spondyloarthritis is distinguishing inflammatory back pain from mechanical back pain.

Inflammatory back pain features:

- Insidious onset (gradual rather than sudden)
- Onset before age 40-45 (later onset is less typical)
- Morning stiffness lasting more than 30 minutes
- Improvement with activity, worsening with rest
- Pain that wakes you up in the second half of the night
- Persisting more than 3 months
- Alternating buttock pain (suggestive of sacroiliitis specifically)

Mechanical back pain features:

- Sudden onset, often associated with specific activity
- Worsening with activity, improving with rest
- Short-lived morning stiffness
- Pain pattern related to position and movement
- Often resolves with conservative management within weeks

The inflammatory pattern, particularly the combination of morning stiffness, improvement with activity, and night pain, is highly suggestive of axial spondyloarthritis and warrants rheumatology evaluation in an HS patient.

Other musculoskeletal features that warrant attention:

- Enthesitis — pain and tenderness at tendon attachment sites, particularly Achilles tendon, plantar fascia, or other characteristic enthesises
- Dactylitis — diffuse sausage-like swelling of an entire finger or toe
- Asymmetric oligoarthritis — inflammation of a few large joints in an asymmetric pattern
- Anterior chest wall pain — particularly sternoclavicular or costochondral pain (relevant for SAPHO)

When to seek rheumatology evaluation

For HS patients, the threshold for rheumatology referral:

Strong indications:

- Inflammatory back pain pattern persisting more than 3 months
- Morning stiffness lasting more than 30 minutes
- Asymmetric joint pain or swelling
- Enthesitis at characteristic sites
- Family history of ankylosing spondylitis, psoriatic arthritis, or other spondyloarthritis
- HLA-B27 positive (if testing has been done)

Moderate indications:

- Recurrent unexplained joint pain
- Chronic back pain with any inflammatory features
- Coexisting features of other inflammatory disease (uveitis, IBD symptoms)

Useful initial assessment by the general practitioner or dermatologist:

- Detailed history of joint pain pattern, duration, response to activity, morning stiffness
- Examination of axial skeleton, sacroiliac joints, peripheral joints, and enthesises
- Inflammatory markers (CRP, ESR) — often elevated but not always
- HLA-B27 testing — strongly associated with axial SpA but not diagnostic alone
- Pelvic X-ray to look for sacroiliitis
- MRI of sacroiliac joints if X-ray is non-diagnostic but suspicion is high

Definitive diagnosis is made by rheumatology, typically using the ASAS (Assessment of SpondyloArthritis international Society) classification criteria or similar frameworks.

Treatment implications

The HS-spondyloarthritis overlap has direct implications for biologic selection.

TNF inhibitors

Adalimumab is approved for HS and for ankylosing spondylitis, non-radiographic axial SpA, and psoriatic arthritis. For a patient with both HS and any of these forms of spondyloarthritis, adalimumab can address both conditions through a single biologic. This is one of the strongest practical advantages of recognizing the comorbidity.

Etanercept and infliximab are approved for spondyloarthritis subtypes and used off-label for HS in some contexts, with variable evidence.

Certolizumab pegol is approved for axial spondyloarthritis and has the advantage of minimal placental transfer, making it the preferred TNF inhibitor for pregnancy planning in patients who need ongoing therapy.

IL-17 inhibitors

Secukinumab is approved for HS and for psoriasis, psoriatic arthritis, ankylosing spondylitis, and non-radiographic axSpA. The full overlap of approved indications makes secukinumab an attractive choice for patients with HS plus any of these spondyloarthritis forms — except where IBD is also present, in which case TNF inhibitors are preferred.

Bimekizumab is approved for HS, psoriasis, psoriatic arthritis, axial spondyloarthritis, and ankylosing spondylitis. The same considerations apply.

For a patient with HS plus inflammatory back pain plus no IBD, an IL-17 inhibitor is an excellent choice. For a patient with HS plus IBD plus inflammatory back pain, a TNF inhibitor is preferred to avoid IBD worsening.

Other treatments

Standard non-biologic spondyloarthritis treatments include:

- NSAIDs as first-line symptomatic and disease-modifying therapy for axSpA
- Conventional synthetic DMARDs (methotrexate, sulfasalazine) for peripheral disease; less effective for axial disease
- JAK inhibitors (tofacitinib, upadacitinib) approved for some forms of SpA

These treatments are managed by rheumatology following standard guidelines.

Physical therapy

Exercise and physiotherapy are foundational for axial spondyloarthritis management, with strong evidence for preventing functional impairment. The exercise programs typically focus on maintaining spinal mobility, posture, and overall fitness. HS does not preclude exercise but requires individualization (lower-friction activities during flares, attention to sweat management). The companion article on triggers and lifestyle covers exercise considerations.

In Germany specifically

The German healthcare pathway for spondyloarthritis assessment:

- Hausarzt (general practitioner) typically initiates assessment and referral
- Rheumatology referral is standard for suspected SpA; rheumatologist availability varies by region
- Imaging (X-ray, MRI of sacroiliac joints) is generally accessible
- HLA-B27 testing is reimbursable under GKV when clinically indicated
- Biologic therapy for SpA is reimbursable under GKV when prescribed within approved indications, with same considerations as for HS

Coordinated care between rheumatology and dermatology improves outcomes when both conditions are present. Larger HS specialty centres in Germany sometimes have collaborative pathways with rheumatology for patients with apparent multi-system inflammatory disease.

Frequently asked questions

Will treating my HS help my joint pain?

If the joint pain is due to spondyloarthritis and the HS treatment is one of the biologics approved for both (TNF inhibitors, secukinumab, bimekizumab), then yes — the same drug addresses both. If the joint pain is from a different cause, HS treatment will not specifically help.

Should I have HLA-B27 testing?

If you have inflammatory back pain features or other features suggesting axial spondyloarthritis, HLA-B27 testing is part of standard workup. Routine testing in all HS patients without joint symptoms is not appropriate. HLA-B27 is associated with but not diagnostic of axial spondyloarthritis; many HLA-B27 positive people never develop disease, and some axSpA patients are HLA-B27 negative.

Can I have spondyloarthritis without back pain?

Yes. Peripheral spondyloarthritis can present with predominant joint or enthesitis symptoms rather than axial features. Some patients have very minimal back pain despite imaging evidence of sacroiliitis.

My MRI showed sacroiliitis. Is that the same as ankylosing spondylitis?

Sacroiliitis on MRI without radiographic changes is the imaging feature of non-radiographic axial spondyloarthritis (nr-axSpA), which is now recognized as part of the axial spondyloarthritis spectrum. Whether it progresses to radiographic disease (ankylosing spondylitis) varies; some patients remain non-radiographic indefinitely. Treatment principles are similar.

Will my HS spondyloarthritis cause permanent damage?

Untreated axial spondyloarthritis can produce structural damage to the spine (fusion of vertebrae) and peripheral joints over years. Effective treatment reduces but does not eliminate this risk. Early recognition and treatment improve long-term functional outcomes, which is the main argument for not ignoring inflammatory back pain in HS patients.

Can I have spondyloarthritis without HLA-B27?

Yes. Approximately 80-90% of patients with ankylosing spondylitis are HLA-B27 positive, but a meaningful minority are HLA-B27 negative. Non-radiographic axSpA and psoriatic arthritis have lower HLA-B27 association rates. The diagnosis is made on combined clinical, laboratory, and imaging criteria, not HLA-B27 alone.

What about uveitis — does that fit in?

Uveitis (eye inflammation) is an extra-articular manifestation of spondyloarthritis. Acute anterior uveitis occurs in approximately 25-40% of patients with axial spondyloarthritis at some point. Patients with HS, joint symptoms, and recurrent painful red eye episodes should be evaluated for the connection. Ophthalmology referral for recurrent uveitis is appropriate, and the link to spondyloarthritis should be mentioned.

Will my HS biologic work for my spondyloarthritis at the HS-recommended dose?

Dosing for the different indications differs. Adalimumab dosing for HS (40 mg weekly after loading) is more intensive than for ankylosing spondylitis (40 mg every two weeks). Bimekizumab dosing varies by indication. The HS dose is typically sufficient or more than sufficient for the SpA indication; specific dose decisions are made with input from both dermatology and rheumatology.

Should I see a rheumatologist as part of my baseline HS workup?

Not routinely, in the absence of symptoms suggesting joint involvement. Baseline HS care does not require rheumatology assessment for asymptomatic patients. Targeted referral when joint or back symptoms suggest spondyloarthritis is appropriate.
Disclaimer. This article is for general education and does not constitute personal medical advice. Diagnosis and management of spondyloarthritis requires evaluation by qualified rheumatological clinicians. Coordination between dermatology and rheumatology is appropriate when both conditions are present or suspected.

References

1. Garg A, Malviya N, Strunk A, et al. Comorbidity screening in hidradenitis suppurativa: Evidence-based recommendations from the US and Canadian Hidradenitis Suppurativa Foundations. - Journal of the American Academy of Dermatology, 2022
2. Schneider-Burrus S et al. High prevalence of hidradenitis suppurativa symptoms in axial spondyloarthritis patients: A possible new extra-articular manifestation. - Seminars in Arthritis and Rheumatism
3. Rondags A et al. High prevalence of hidradenitis suppurativa symptoms in axial spondyloarthritis patients. - British Journal of Dermatology
4. Tzellos T, Zouboulis CC. Review of Comorbidities of Hidradenitis Suppurativa: Implications for Daily Clinical Practice. - Dermatology and Therapy, 2020
5. Aksentijevich I, Kastner DL. Genetics of monogenic autoinflammatory diseases: past successes, future challenges. - Nature Reviews Rheumatology