Nail Arthritis: Types, Symptoms, Diagnosis, and Treatment

What is nail arthritis?

Nail arthritis refers to the manifestation of inflammatory joint diseases, most commonly psoriatic arthritis, within the nail unit and the surrounding distal finger or toe joints, leading to characteristic changes in nail appearance and potential functional impairment.

Understanding Nail Arthritis

Nail arthritis, also known as arthritic onychopathy, is a specific presentation of systemic inflammatory conditions where the immune system mistakenly attacks healthy tissues, including those in and around the nails. While various forms of arthritis can cause nail changes, the term "nail arthritis" most commonly refers to the nail involvement seen in psoriatic arthritis (PsA), a chronic autoimmune disease that affects the skin, joints, and entheses (where tendons or ligaments attach to bone). The nails can serve as a crucial diagnostic indicator, often preceding or co-occurring with joint symptoms.

Types of Arthritis Affecting the Nails

While PsA is the primary culprit, other arthritic conditions can also present with nail changes, though less specifically or commonly.

• Psoriatic Arthritis (PsA): This is by far the most significant form of arthritis associated with nail changes. Up to 90% of individuals with PsA experience nail involvement at some point, and in about 5-10% of cases, nail changes are the first symptom to appear, sometimes years before joint pain. The nail involvement in PsA is closely linked to inflammation of the distal interphalangeal (DIP) joints – the small joints closest to the fingertips or toes – and the nail matrix (where the nail grows from) and nail bed (the tissue under the nail plate).
• Osteoarthritis (OA): While primarily a "wear-and-tear" degenerative joint disease, OA can affect the DIP joints, leading to bony enlargements (Heberden's nodes). These structural changes can sometimes alter nail growth or appearance, though they are not due to the inflammatory processes seen in PsA.
• Rheumatoid Arthritis (RA): Less common, but severe RA can sometimes lead to nail changes such as ridging, thinning, or even nail loss, often due to vasculitis (inflammation of blood vessels) or secondary infections.

How Arthritis Affects the Nails

The pathology of nail arthritis, particularly in PsA, stems from chronic inflammation. The nail unit is a complex structure closely integrated with the underlying bone and joint.

• Inflammation of the Distal Interphalangeal (DIP) Joint: The close proximity of the DIP joint to the nail matrix and nail bed means that inflammation in the joint can directly impact the structures responsible for nail growth and health.
• Inflammation of the Nail Matrix: The nail matrix is the tissue underneath the cuticle where nail cells are produced. Inflammation here disrupts normal keratinization, leading to abnormalities in the nail plate itself, such as pitting or ridging.
• Inflammation of the Nail Bed: The nail bed supports the nail plate. Inflammation in this area can cause changes like onycholysis (separation of the nail from the bed) or "oil drop" spots.
• Enthesitis: This is inflammation at the sites where tendons or ligaments attach to bone. In PsA, enthesitis can occur around the nail, contributing to nail changes and pain.

Common Nail Symptoms

Nail changes in arthritis are varied and can affect one or multiple nails. They are often a key indicator for diagnosis.

• Nail Pitting: Small, pinpoint depressions or dents on the surface of the nail plate, resembling the surface of a thimble. This is one of the most common and characteristic signs.
• Onycholysis: The separation of the nail plate from the nail bed, typically starting at the free edge and progressing inward. This can create a white or yellowish area under the nail and increase the risk of infection.
• Oil Drop or Salmon Patches: Translucent, yellowish-brown or reddish-brown discolorations under the nail plate, resembling a drop of oil. These are highly specific to psoriatic nail involvement.
• Nail Thickening (Subungual Hyperkeratosis): An accumulation of scaly debris under the nail, causing the nail plate to lift and thicken. This can be painful and lead to difficulty trimming nails.
• Transverse Grooves (Beau's Lines): Horizontal depressions across the nail plate, indicating a temporary halt in nail growth, often due to systemic illness or trauma.
• Nail Discoloration: Nails may appear yellow, brown, or crumbly.
• Nail Ridging: Longitudinal or transverse ridges can appear on the nail surface.

Associated Joint Symptoms

Nail arthritis rarely occurs in isolation. It is typically accompanied by, or precedes, specific joint involvement.

• Distal Interphalangeal (DIP) Joint Involvement: Pain, swelling, stiffness, and tenderness in the small joints closest to the fingertips and toes. This is particularly common in PsA and often directly correlates with nail involvement on the same digit.
• Dactylitis ("Sausage Digit"): Swelling of an entire finger or toe, giving it a sausage-like appearance. This is due to inflammation of the joints, tendons, and surrounding tissues within the digit.
• Enthesitis: Pain and tenderness at the sites where tendons or ligaments attach to bone, such as the Achilles tendon or plantar fascia, or around the nail itself.
• Morning Stiffness: Joint stiffness that is worse in the morning or after periods of inactivity, typically lasting for more than 30 minutes.

Diagnosis

Diagnosing nail arthritis involves a comprehensive approach, as nail changes can also be caused by fungal infections, trauma, or other conditions.

• Clinical Examination: A thorough physical examination by a rheumatologist or dermatologist is crucial. The physician will examine the nails, skin (looking for psoriasis plaques), and joints for signs of inflammation.
• Patient History: Detailed information about symptoms, family history of psoriasis or arthritis, and onset of symptoms helps differentiate conditions.
• Imaging Studies:
  • X-rays: Can show joint erosion, joint space narrowing, and new bone formation characteristic of PsA, particularly in the DIP joints.
  • Ultrasound and MRI: More sensitive imaging techniques that can detect inflammation in the joints, tendons, and entheses, even before structural damage is visible on X-rays.
• Blood Tests: While there's no single diagnostic blood test for PsA, tests can help rule out other conditions (e.g., rheumatoid factor and anti-CCP antibodies to exclude RA) and assess inflammatory markers (e.g., C-reactive protein, erythrocyte sedimentation rate).
• Nail Biopsy: Rarely, a nail biopsy may be performed to differentiate between conditions, though it's often avoided due to potential for pain and scarring.

Management and Treatment

Treatment for nail arthritis is primarily aimed at managing the underlying inflammatory condition, typically PsA. A multidisciplinary approach involving rheumatologists, dermatologists, and physical therapists is often most effective.

• Medical Treatments:
  • Nonsteroidal Anti-inflammatory Drugs (NSAIDs): Used for pain and inflammation relief, particularly for mild symptoms.
  • Disease-Modifying Antirheumatic Drugs (DMARDs): Medications like methotrexate, sulfasalazine, or leflunomide suppress the immune system to reduce joint and skin inflammation.
  • Biologic Agents: These are advanced therapies that target specific components of the immune system involved in inflammation (e.g., TNF inhibitors, IL-17 inhibitors, IL-23 inhibitors). They are highly effective for severe PsA with significant joint and nail involvement.
  • Topical Treatments: Corticosteroids, vitamin D analogues, and calcineurin inhibitors can be applied directly to the nail and surrounding skin to reduce inflammation and improve nail appearance.
• Physical and Occupational Therapy:
  • Joint Protection Techniques: Learning to modify activities to reduce stress on affected joints.
  • Range of Motion Exercises: Gentle exercises to maintain joint flexibility and prevent stiffness.
  • Strengthening Exercises: To support affected joints and improve functional capacity.
  • Adaptive Equipment: Tools to assist with daily tasks that may be difficult due to joint pain or nail changes.
• Lifestyle Modifications:
  • Nail Care: Keeping nails trimmed, avoiding trauma, and keeping them clean can prevent worsening of symptoms and secondary infections.
  • Moisturizing: Regular moisturizing of hands and feet can improve skin and nail health.
  • Avoiding Triggers: Identifying and avoiding factors that exacerbate psoriasis (e.g., stress, certain medications, skin injury).

Outlook and Living with Nail Arthritis

Nail arthritis is a chronic condition, and its impact can range from cosmetic concerns to significant functional impairment, especially if the underlying joint disease is not well-controlled. Early diagnosis and consistent, appropriate treatment are crucial to prevent progressive joint damage and improve quality of life. While nail changes can be challenging to treat and may take a long time to improve, effective therapies exist that can reduce inflammation, alleviate symptoms, and slow disease progression, allowing individuals to maintain an active and fulfilling life. Regular follow-ups with healthcare providers are essential for ongoing management and adjustment of treatment plans as needed.