Dactylitis is a valuable clue in the differential diagnosis of arthritis. Compared with the wider spectrum in children, sausage-shaped digits have only a few known causes in adults: Reiter's syndrome, psoriatic arthritis, sarcoidosis, flexor tendon sheath infections, and gout.
Dactylitis is caused by uncontrolled inflammation that results from spondyloarthropathies, and can be associated with flaring of the underlying joint disease.
The swelling is diffuse and continuous throughout the tissue, affecting tendons, ligaments, synovium — the space that contains the joints and joint capsule — and adjacent soft tissue.
In terms of why there’s such a strong association between dactylitis and psoriatic arthritis, there’s still no definitive answer, It isn’t clear why dactylitis happens, but it is likely that its origin is related to the fact that patients with psoriatic arthritis have a tendency to develop inflammation of tendons and the surrounding tendon sheaths in addition to inflammation of the actual joints.
Viral infection: human parvovirus (especially B19), enterovirus, adenovirus, Epstein-Barr, coxsackievirus (A9, B2, B3, B4, B6), cytomegalovirus, rubella, mumps, hepatitis B, varicella-zoster virus (human herpes virus 3), human immunodeficiency virus
Indirect bacterial infection (reactive arthritis): Neisseria gonorrhoeae (gonorrhea), bacterial endocarditis, Campylobacter species, Chlamydia species, Salmonella species, Shigella species, Yersinia species, Tropheryma whippelii (Whipple's disease), group A streptococci (rheumatic fever)
Direct bacterial infection: N. gonorrhoeae, Staphylococcus aureus, gram-negative bacilli, bacterial endocarditis
Other infections: Borrelia burgdorferi (Lyme disease), Mycobacterium tuberculosis (tuberculosis), fungi
Crystal-induced synovitis: gout, pseudogout (calcium pyrophosphate deposition disease), hydroxyapatite
Systemic rheumatic disease: rheumatoid arthritis, systemic lupus erythematosus, polymyositis/dermatomyositis, juvenile rheumatoid arthritis, scleroderma, Sjögren's syndrome, Behçet's syndrome, polymyalgia rheumatica
Systemic vasculitis disease: Schönlein-Henoch purpura, hypersensitivity vasculitis, polyarteritis nodosa, Wegener's granulomatosis, giant cell arteritis
Spondyloarthropathies: ankylosing spondylitis, psoriatic arthritis, inflammatory bowel disease, reactive arthritis (Reiter's syndrome)
Endocrine disorders: hyperparathyroidism, hyperthyroidism, hypothyroidism
Malignancy: metastatic cancer, multiple myeloma
Others: osteoarthritis, hypermobility syndromes, sarcoidosis, fibromyalgia, osteomalacia, Sweet's syndrome, serum sickness