# Spondyloarthritis and Hidradenitis Suppurativa (Acne Inversa): The Underdiagnosed Joint Involvement

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Language: en
Category: Treatments
Published: 2026-05-21
Last updated: 2026-05-21
Last editorially reviewed: 2026-05-21
Next scheduled review: 2027-05-21

Author: Dr. rer. nat. Dennis Alexander Kwiatkowski (Biochemist, Scientific Writer and Pharma Expert)
Scientific editor: Dr. rer. nat. Dennis Alexander Kwiatkowski
Reviewer qualifications: Biochemist, Scientific Writer and Pharma Expert
Review scope: Scientific literature, clinical guidelines, sources, and editorial clarity
Clinical reviewer: No independent clinical review
Tags: Acne Inversa, Hidradenitis Suppurativa, HS, Treatments, Spondyloarthritis, axial SpA, ankylosing spondylitis, psoriatic arthritis, SAPHO, PASS syndrome, comorbidities

> Joint involvement in HS is frequently overlooked, despite being present in a substantial proportion of patients. This article covers axial spondyloarthritis, SAPHO syndrome, PASS, and the question of when back pain in an HS patient warrants a 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 group of inflammatory joint diseases that includes axial spondyloarthritis, ankylosing spondylitis (Bechterew's disease), and psoriatic arthritis – occurs considerably more often in HS patients than in the general population. The IL-17 inflammatory pathway, which is central to HS, is also central to spondyloarthritis, providing a clear biological link. Nevertheless, most HS patients with joint complaints are not screened for spondyloarthritis, and a treatment that could address both conditions is often not considered.

This article covers what spondyloarthritis is, what is known about its frequency in HS, the specific syndromes that link HS with musculoskeletal inflammation (including SAPHO syndrome and the PASS pattern), the symptoms that warrant rheumatological evaluation, and the treatment implications when both conditions are present simultaneously.

> **For educational purposes only.** Diagnosing and treating spondyloarthritis requires rheumatological evaluation. This article describes general principles, not personal recommendations.

## Key Findings

- The prevalence of spondyloarthritis in HS populations is reported in various studies at 1.5% to 40%, compared with <2% in the general population. The wide range reflects differing 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 with musculoskeletal inflammation, including SAPHO (synovitis, acne, pustulosis, hyperostosis, osteitis) and the PASS pattern (pyoderma gangrenosum, acne, suppurative hidradenitis, spondyloarthritis).
- IL-17 inhibitors (secukinumab, bimekizumab), which are approved for HS, are also approved for spondyloarthritis. TNF inhibitors are approved for both. This treatment overlap means a single biologic can address both conditions in a patient who has both.
- Clinical features that should prompt rheumatological evaluation in an HS patient include inflammatory back pain, morning stiffness lasting more than 30 minutes, joint pain or swelling that goes beyond mechanical causes, and a family history of axial spondyloarthritis or psoriasis.

## What Spondyloarthritis Actually Is

Spondyloarthritis (SpA) is a group of inflammatory rheumatic diseases that share certain clinical and biological features. Conditions within this group include:

- **Axial spondyloarthritis (axSpA)** – characterized by inflammation of the spine and sacroiliac joints. This includes ankylosing spondylitis (the historical term for radiographic axSpA, when changes are visible on conventional X-ray) and non-radiographic axSpA (in which MRI shows inflammation before X-ray changes appear).
- **Psoriatic arthritis** – an inflammatory arthritis associated with psoriasis (or sometimes preceding it). Can affect peripheral joints, entheses (where tendons attach to bone), or the axial skeleton.
- **Peripheral spondyloarthritis** – affects 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.

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

In the context of HS, **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 reported inconsistently, reflecting the difficulty of diagnosing spondyloarthritis (which requires a combination of clinical features and imaging or laboratory criteria) and the heterogeneity of the HS populations studied.

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

**Comparison with the general population.** The prevalence of spondyloarthritis in the general population is around 0.5% to 2%, depending on definition, geographic location, and ethnic background. Even the lower HS estimates therefore represent at least a 2- to 3-fold increase; the higher estimates reflect a substantially elevated burden in HS-specialized 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 proportion of HS patients – suggesting that the diagnostic gap, rather than the absence of disease, explains much of the underdiagnosis seen in routine care.

**The 2021 evidence-based screening recommendations** from the US and Canadian Hidradenitis Suppurativa Foundations explicitly include spondyloarthritis among the 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 overall not shown a strong association with HS, suggesting that the shared pathway operates downstream of genetic susceptibility rather than involving identical genetic causes.

## The Specific Syndromes to Know

Several named syndromes link HS with musculoskeletal inflammation, reflecting the broader inflammatory connection.

### SAPHO Syndrome

SAPHO (synovitis, acne, pustulosis, hyperostosis, osteitis) is a rare inflammatory syndrome that combines sterile bone and joint inflammation with a neutrophilic skin disease. The skin component most often includes severe acne (acne conglobata, acne fulminans), palmoplantar pustulosis, or – in some patients – HS.

**Clinical features:**

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

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

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

### PASS Syndrome (and Related Autoinflammatory Clusters)

PASS – pyoderma gangrenosum, acne, suppurative hidradenitis, spondyloarthritis – describes a syndrome in which these conditions occur together 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 an underlying dysregulation of the inflammasome and neutrophilic inflammation. They are rare but well documented and provide a framework for understanding how HS fits into a broader spectrum of neutrophilic and inflammatory diseases.

**Clinical significance:** In an HS patient who develops pyoderma gangrenosum (a distinct, characteristic skin condition with rapidly progressing ulcerating lesions) or severe nodulocystic acne along with joint complaints, evaluation within this framework should be considered. Treatment typically involves systemic immunosuppression and biologic therapy.

### Hidradenitis Suppurativa with Axial Spondyloarthritis (No Specific Syndrome Name)

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 comorbidities that share inflammatory pathways but do not constitute a distinct disease entity.

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

## Recognizing Inflammatory Back Pain

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

**Features of inflammatory back pain:**

- **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 movement, worsening with rest**
- **Pain that wakes the patient in the second half of the night**
- **Persisting for more than 3 months**
- **Alternating buttock pain** (specifically suggestive of sacroiliitis)

**Features of mechanical back pain:**

- Sudden onset, often related to a specific activity
- Worsens with movement, improves with rest
- Short-lived morning stiffness
- Pain pattern related to position and movement
- Often improves within weeks with conservative treatment

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

**Other musculoskeletal features that require attention:**

- **Enthesitis** – pain and tenderness at tendon attachment sites, particularly the Achilles tendon, plantar fascia, or other characteristic entheses
- **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 to SAPHO)

## When to Seek Rheumatological Evaluation

For HS patients, the following threshold applies for a rheumatology referral:

**Strong indications:**

- Pattern of inflammatory back pain persisting for 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 positivity (if testing has been performed)

**Moderate indications:**

- Recurrent, unexplained joint pain
- Chronic back pain with inflammatory features
- Accompanying features of other inflammatory diseases (uveitis, IBD symptoms)

**Useful initial assessment** by the primary care physician or dermatologist:

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

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

## Treatment Implications

The overlap between HS and spondyloarthritis has direct implications for biologic selection.

### TNF Inhibitors

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

Etanercept and infliximab are approved for spondyloarthritis subtypes and are 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 require ongoing therapy.

### IL-17 Inhibitors

Secukinumab is approved for HS as well as for psoriasis, psoriatic arthritis, ankylosing spondylitis, and non-radiographic axSpA. The complete overlap of approved indications makes secukinumab an attractive choice for patients with HS plus one of these forms of spondyloarthritis – except when 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 preferable to avoid worsening the IBD.

### Other Treatments

Standard, non-biologic spondyloarthritis treatments include:

- **NSAIDs** as first-line symptomatic and disease-modifying therapy in 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 according to current guidelines.

### Physical Therapy

Exercise and physical therapy are fundamental to managing axial spondyloarthritis, with strong evidence for preventing functional limitations. 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 considerations regarding exercise.

## Specifically in Germany

The German care pathway for spondyloarthritis evaluation:

- **The primary care physician** typically initiates the evaluation and referral
- **Referral to rheumatology** is standard when SpA is suspected; the availability of rheumatologists varies by region
- **Imaging** (X-ray, MRI of the sacroiliac joints) is generally accessible
- **HLA-B27 testing** is reimbursable under statutory health insurance (GKV) when clinically indicated
- **Biologic therapy for SpA** is reimbursable under statutory health insurance when prescribed within approved indications, with the same considerations as for HS

Coordinated care between rheumatology and dermatology improves outcomes when both conditions are present. Larger HS specialty centers in Germany sometimes have cooperative care pathways with rheumatology for patients with evident multisystem 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 conditions (TNF inhibitors, secukinumab, bimekizumab), then yes – the same medication addresses both. If the joint pain has a different cause, the HS treatment will not specifically help.

**Should I get HLA-B27 testing done?**

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

**Can I have spondyloarthritis without back pain?**

Yes. Peripheral spondyloarthritis can present with predominantly 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 hallmark 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. The treatment principles are similar.

**Will my HS-spondyloarthritis cause permanent damage?**

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

**Can I have spondyloarthritis without HLA-B27?**

Yes. About 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 rates of HLA-B27 association. The diagnosis is made based on combined clinical, laboratory, and imaging criteria, not on HLA-B27 alone.

**What about uveitis – does that fit in?**

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

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

Dosing differs across indications. The adalimumab dose 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 generally sufficient or more than sufficient for the SpA indication; specific dosing decisions are made with input from both dermatology and rheumatology.

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

Not routinely, unless symptoms suggestive of joint involvement are present. Baseline HS care does not require rheumatological evaluation in asymptomatic patients. A targeted referral, when joint or back symptoms suggest spondyloarthritis, is appropriate.

> **Disclaimer.** This article is for general educational purposes and does not constitute personal medical advice. Diagnosing and treating spondyloarthritis requires evaluation by qualified rheumatology professionals. 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