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Psoriatic arthritis
New biologic agents prove successful
BY Monique Camerlain, MD
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Amanda, a 28-year-old secretary, has
had psoriasis for 8 years. Over the last 4 months, she's complained
about pain and swelling of her wrists, metacarpophalangeal joints
(MCP), knees, ankles and metatarsophalangeal joints (MTP). She lives
alone, reports difficulties in her romantic relationships and is becoming
depressed.
Presentation
Physical examination
- nail pitting
- scaly lesions on her scalp, knees
and elbows, breasts and genitals
- pain on pressure, and swelling of
the symptomatic joints, consistent with psoriatic arthritis
with a symmetric polyarthritic pattern
Investigations
- normal blood count
- negative rheumatoid factor (RF)
- elevated sedimentation rate
- soft tissue swelling on the x-rays
of her hands and feet
Diagnosis
and treatment
Amanda has psoriatic arthritis (PsA). Naproxen at 500 mg twice
daily was of little help, so she was put on methotrexate,
which was progressively increased to weekly 25 mg subcutaneously
-- with limited success. On both sides, her MCP 2 and 3, knees,
ankles and MTP 2, 3 and 4 remained swollen. Considering her
skin condition and the number of active joints, an anti-tumour
necrosis factor (anti-TNF) was suggested, with the hope that
it would resolve both the arthritis and cutaneous lesions,
as well as halt the progression of articular damage and improve
her quality of life.
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Making the case
Psoriasis is a chronic inflammatory disease of the skin, affecting
about 1 million people in Canada. Its name is derived from "psora,"
the Greek word for scab. The association between arthritis and psoriasis
was noted back in the 19th century -- indeed, up to 40% of people
with psoriasis develop PsA, usually within 5-10 years after onset
of the cutaneous disease. Arthritis precedes the skin lesions in
about 15% of patients, and it appears simultaneously in another
20%.
PsA is progressive and erosive in 50% of cases, and it can lead
to functional impairment and decreased quality of life. Patients
with psoriasis have nearly 2 times the average level of comorbidities,
including diabetes, gastrointestinal disorders, hepatotoxicity,
hypertension and cardiac disease. They also have an increased rate
of depression, suicide and alcoholism, and 72% report difficulties
in their sexual life. In addition, these people often suffer discrimination
in public places because their skin lesions are thought to be contagious.
PsA raises the risk of death, which is even higher if the sedimentation
rate is elevated or if there's radiological evidence of joint damage.
Mechanism of disease
Family investigations, genome-wide scans, human leukocyte antigen
and candidate gene studies have demonstrated a genetic link with
PsA, but immunologic factors and the environment also play a role.
The disease is almost certainly immune-mediated, although the exact
mechanism isn't well understood yet. Synovium affected by PsA shows
infiltration with T cells, B cells and macrophages, and is also
characterized by an upregulation of leukocyte homing receptors.
Cytokine production in the synovium resembles that in psoriatic
skin lesions and in the synovium with rheumatoid arthritis (RA),
having predominantly a Th1 pattern.
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