Psoriatic arthritis of the hand: dactylitis and nail changes
Psoriatic arthritis (an inflammatory arthritis that occurs in people with psoriasis, a skin disease) classically gives dactylitis, swelling of a whole finger into a sausage shape, with nail changes.
Remember
A sausage-shaped swollen finger with nail changes such as onycholysis (the nail lifting away from its bed) is the characteristic hand finding of psoriatic arthritis, and the swelling comes from inflammation of tendons, joints and soft tissues together.
Psoriatic arthritis is an inflammatory arthritis that occurs in people with psoriasis, a skin disease. In the hand, its most distinctive feature is dactylitis, which is swelling of a whole finger or toe so that it looks like a sausage. The swelling is fusiform, meaning spindle-shaped, fat in the middle and tapering at each end.
Dactylitis does not come from one inflamed joint. The flexor tendons (the tendons that bend the finger), the joints and the soft tissues of the finger are inflamed together, so the swelling runs the full length of the finger instead of sitting at one knuckle. There is also inflammation where the tendons attach to bone, called enthesitis.
The nails give the second clue. Pitting means small pits in the nail surface, and onycholysis means the nail lifting away from its bed. A sausage-shaped finger and a damaged nail in someone with psoriasis should make you think of psoriatic arthritis rather than rheumatoid arthritis (inflammation centred on the joint lining).
Rheumatoid arthritis tends to give symmetrical swelling of the small joints with deformities such as ulnar deviation (the fingers drifting towards the little-finger side at the knuckles), and osteoarthritis (wear of the cartilage on the joint ends) gives bony swellings of the finger joints. Psoriatic arthritis can also involve the distal interphalangeal joints (the joints nearest the fingertips), so that feature on its own is less specific.
Key facts
- Dactylitis
- swelling of a whole finger into a sausage shape, from inflammation of the flexor tendons, joints and soft tissues together.
- Nail changes
- pitting and onycholysis (the nail lifting away from its bed) are typical of psoriatic arthritis and go with psoriasis.
- Stiffness
- prolonged morning stiffness suggests inflammatory arthritis, whereas osteoarthritis stiffness usually lasts under about 30 minutes.
- Treatment step
- NSAIDs (non-steroidal anti-inflammatory drugs, such as ibuprofen) help mild symptoms, and disease-modifying anti-rheumatic drugs are used for moderate to severe disease.
- Biological treatments
- injected medicines that are kept for when disease-modifying anti-rheumatic drugs do not help.
- Prognosis
- dactylitis is a distinctive feature of psoriatic arthritis and is linked to a poorer prognosis.
Exam traps
- Ulnar deviation (the fingers drifting towards the little-finger side at the knuckles) does not point to psoriatic arthritis, because it is typical of long-standing rheumatoid arthritis and reflects tendon slippage and joint damage in that disease.
- Firm lumps under the skin (rheumatoid nodules) are absent in psoriatic arthritis, so they would point towards rheumatoid disease instead.
- Osteoarthritis can look tempting because psoriatic arthritis also involves the joints nearest the fingertips, but osteoarthritis does not inflame the tendons and soft tissues of the whole finger or separate the nail.
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