Pathogenesis and etiology
The exact causes of the disease remain unclear. It is generally accepted to be based on a multifactorial model that includes genetic predisposition, immunological disorders, and environmental triggers.
Tumor necrosis factor alpha (TNFα) is a key mediator in the destruction of joint tissues. Its effects impact various structures:
- Cells: stimulates fibroblast proliferation and activates the endothelium.
- Enzymes: increases the expression of matrix metalloproteinases and collagenase production, leading to cartilage destruction.
- Inflammation: enhances the synthesis of prostaglandin E2 and chemokines.
- Bone tissue: activates osteoclasts, causing bone resorption.
Clinical presentation of articular syndrome
The onset of the disease can be gradual (with fatigue, weight loss, myalgia) or acute (with severe pain, morning stiffness, and swelling). In the majority of patients (about 80%), asymmetric mono- or oligoarthritis is observed. Typical localization includes the distal and proximal interphalangeal joints of the hands, as well as the knee joints.
Specific signs of joint involvement:
- Involvement of "exception joints": inflammation of the first interphalangeal joint of the thumb and the proximal interphalangeal joint of the fifth finger.
- Axial arthritis: simultaneous involvement of all joints of a single digit.
- Dactylitis: inflammation of the flexor tendon sheaths, causing uniform swelling of the digit ("sausage" digit).
- Mutilating arthritis: a severe form with destruction of the phalanges, leading to shortening of the fingers ("telescoping finger" sign) and deformity ("lorgnette hand").
Diagnostics
In pediatrics, the diagnosis is often established using the Vancouver criteria (1989). It is based on a combination of arthritis with cutaneous manifestations or specific "minor" signs.
The difficulty lies in the fact that in children, skin lesions are often subtle or appear after the articular syndrome. The physician must carefully examine the scalp, inguinal, and umbilical areas for hidden plaques.
Minor diagnostic criteria:
- Nail changes ("pitting" sign, onycholysis).
- Family history of psoriasis (1st- or 2nd-degree relatives).
- Psoriasiform rash.
- Dactylitis.
The diagnosis is considered definite if arthritis is combined with a typical rash or three minor criteria. A probable diagnosis is made in the presence of arthritis and two minor criteria.
Differential diagnosis
Psoriatic arthritis in children should be differentiated from other seronegative spondyloarthritides:
- Reiter's syndrome (reactive arthritis): in addition to a possible rash resembling psoriasis, it is characterized by the triad of symptoms: arthritis, conjunctivitis, urethritis (or diarrhea).
- Ankylosing spondylitis (Bechterew's disease): differs by pronounced pain and stiffness in the lumbosacral spine, spreading from bottom to top, bilateral symmetrical sacroiliitis, and the absence of cutaneous manifestations of psoriasis. In addition, Bechterew's disease is characterized by a rapid response to indole and pyrazolone derivatives.
To memorize the minor diagnostic criteria: "Nails, Relatives, Rash, Sausage" (nail changes, family history of psoriasis, psoriasiform rash, dactylitis — "sausage" digit).
Class and exam questions
What is the characteristic feature of disease onset in children compared to adults?
In half of the cases in children, arthritis begins before the appearance of typical skin rashes, which are often mild or atypical.
What is dactylitis?
This is inflammation of the tendon sheaths (tenosynovitis) leading to uniform swelling of the entire digit, giving it a sausage-like appearance.
What criteria are used to diagnose juvenile PsA?
Vancouver criteria (1989) are used, evaluating the presence of arthritis in combination with a typical rash or a set of "minor" signs (dactylitis, nail changes, burdened heredity, etc.).
What else to study on this topic
- Radiological changes in juvenile psoriatic arthritis
- Principles of therapy for juvenile psoriatic arthritis
- Clinical features of mutilating arthritis
- The relationship between TNFα and other rheumatic diseases
Master the entire topic in the Pediatrics course
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Other topics of «Chapter 9. Rheumatic Diseases»
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