Dactylitis

Dactylitis is the inflammation of a finger or toe. Dactylitis is a typical symptom of seronegative spondyloarthritis (e.g. psoriatic arthritis, reactive arthritis/Reiter's syndrome).

Pathophysiologically, a close connection between enthesitis and dactylitis is assumed. Lateral ligaments, which serve to stabilize the toes and fingers, have a similar cellular composition to other entheses.

Dactylitis leads to clumsy, distended and thickened fingers, so-called sausage fingers. It occurs preferentially in areas with increased mechanical stress, usually affects the 4th toe and is an important diagnostic criterion for spondylarthritis (SpA). In the acute stage, redness and hyperthermia are evident, whereas chronic dactylitis is often asymptomatic. The incidence is around 14% for patients with SpA and 50% for patients with psoriatic arthritis (PsA).

The diagnosis is simple - clinically, there is diffuse swelling of entire fingers or toes or between two joint planes. Dactylitis manifests itself in almost all SpAs and is often a decisive diagnostic criterion - the presence of dactylitis can confirm an initially high suspicion of axial spondyloarthritis if the HLA-B27 status is positive and dactylitis is also a decisive secondary criterion in the CASPAR criteria for the diagnosis of PsA.

Imaging: Sonographic evaluation of dactylitis reveals tendinitis of the finger or toe flexors in almost 95% of patients and synovitis in at least one joint in about 40%. In addition, up to 80% show diffuse swelling of the subcutis around the tendon.

Dactylitis can therefore be divided into three phases. "In the early phase there is tendosynovitis and diffuse soft tissue swelling, in the intermediate phase there is joint involvement and in the late phase synovial hypertrophy dominates". MRI can also relatively often show osteitis".

The most common differential diagnosis is arthritis urica, but osteomyelitis, bone sarcoidosis, tuberculosis and an infection with Mycobacterium marinum must also be differentiated.

Due to the high risk of recurrence, optimal drug therapy and close monitoring of dactylitis are essential.

Local infiltration with cortisone is also a treatment option for dactylitis. "As the flexor tendon is very thin, cortisone infiltration should preferably be ultrasound-guided in order to avoid tendon rupture." In his experience, the effect lasts for at least three months. A study by Girolimetto et al. confirmed that local cortisone infiltration significantly improves pain symptoms, local swelling, function and the Leeds Dactylitis Instrument (LDI) Basic Score compared to systemic NSAID therapy (Girolimetto N et al. 2016) Effectiveness of steroid injection for hand psoriatic dactylitis: results from a multicentre prospective observational study Clin Rheumatol 39: 3383-92 24.

MTX provides a benefit in patients with early-stage PsA: dactylitis symptoms disappeared in around 60% of patients and the LDI-Basic-Score decreased significantly. All biologics, Janus kinase inhibitors and apremilast approved to date for the treatment of SpA and PsA are effective in the treatment of dactylitis according to approval studies (McGonagle D et al. 2019). However, there is a lack of direct comparative studies and dactylitis was only examined as a secondary outcome parameter in each case.

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