Hidradenitis Suppurativa (HS) is a chronic inflammatory skin condition characterized by painful, recurring nodules, abscesses, and tunnels that typically form in inverse areas like the armpits and groin. While primarily a skin disorder, HS is now understood to be a systemic disease, meaning the underlying inflammation affects the entire body. This widespread inflammation links the skin condition to other health issues, including the development of joint pain and arthritis. The shared inflammatory process, driven by immune system overactivity, affects both the skin and the joints.
The Confirmed Connection: HS-Associated Arthropathy
The joint pain experienced by many with HS is a recognized comorbidity, often classified as HS-associated arthropathy or arthritis. This condition is part of a larger group of inflammatory joint diseases known as Spondyloarthritis, which includes psoriatic arthritis and ankylosing spondylitis. Patients with HS are estimated to have a three-fold increased risk of developing inflammatory arthritis compared to the general population. The common link driving this association is the overproduction of pro-inflammatory cytokines, which are signaling proteins in the immune system. Specific cytokines, such as Tumor Necrosis Factor-alpha (TNF-alpha) and Interleukin-17 (IL-17), are elevated in both HS skin lesions and the synovium, the tissue lining the joints. These chemical messengers act as shared inflammatory drivers, simultaneously fueling the skin disease and causing inflammation, pain, and stiffness in the joints.
Types of Joint Involvement and Affected Areas
The joint pain associated with HS can manifest in different ways. The inflammation is categorized into two main types: peripheral arthritis, which affects the limbs, and axial arthritis, which involves the spine and pelvis. Peripheral arthritis typically presents as an asymmetric oligoarthritis, meaning it affects a few joints on one side of the body, most commonly involving large joints like the knees and wrists. This joint inflammation is usually non-deforming, but it causes significant pain and swelling.
Axial involvement focuses on the spine and the sacroiliac joints, which connect the lower spine to the pelvis. This manifestation often causes inflammatory back pain, characterized by stiffness and discomfort that is worse in the morning or after periods of rest. Other specific manifestations are enthesitis and dactylitis. Enthesitis is the inflammation where tendons or ligaments attach directly to the bone, frequently causing pain in areas like the heel or chest wall. Dactylitis is the uniform swelling of an entire digit due to inflammation of the joints and tendons within it.
Differentiating Joint Pain Causes in HS Patients
Determining if joint pain is inflammatory and linked to HS is important because treatment protocols differ significantly based on the underlying cause. Inflammatory joint pain, such as HS-associated arthropathy, is differentiated from mechanical pain, like osteoarthritis, by its pattern. Inflammatory pain is typically worse with rest, improves with activity, and is accompanied by significant morning stiffness that can last for hours. In contrast, mechanical pain is usually worse with movement and better with rest.
To confirm the inflammatory nature, physicians use blood tests to look for elevated levels of acute phase reactants, such as C-reactive protein (CRP) and Erythrocyte Sedimentation Rate (ESR). These markers indicate systemic inflammation, supporting a diagnosis of inflammatory arthritis. Imaging techniques, including X-rays and Magnetic Resonance Imaging (MRI), further aid the diagnostic process by revealing structural changes characteristic of Spondyloarthritis, such as sacroiliitis or the formation of new bone.
Management Strategies for Inflammatory Joint Pain
The primary goal of managing inflammatory joint pain in HS patients is to control the underlying systemic inflammation, which addresses both the skin and the joint symptoms. For mild cases, initial treatment may include non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen, to reduce pain and swelling. However, these medications only provide symptomatic relief and do not stop the progression of the inflammatory disease.
The most effective treatment for HS-associated arthropathy involves systemic therapies that modulate the immune response. Biologics, particularly Tumor Necrosis Factor (TNF) inhibitors, are frequently used because they target the specific inflammatory proteins shared by both conditions. By blocking TNF-alpha, these medications significantly improve both HS skin lesions and joint inflammation. Traditional Disease-Modifying Anti-Rheumatic Drugs (DMARDs) may also be used in conjunction with biologics. A collaborative approach between a dermatologist and a rheumatologist is recommended for optimal management.