Seven subtypes – only diagnose when symptoms for at least 3 months:

• Oligo (persistent or extended) – Arthritis affecting up to four joints during the first six months of disease. If subsequently more than four joints are affected the term extended oligoarthritis is used, otherwise the term persistent oligoarthritis is used. This is the most common pattern (50% of all JIA) and usually involves large joints of the lower limbs, especially knees. These children have the best prognosis but are at high risk of asymptomatic uveitis (30%, and risk highest in monoarthritis!) and therefore must be screened regularly. In aggressive disease, can develop within 3 months of presentation. Girls mostly ankles, knees or wrists, 50% will be ANA positive and particularly associated with chronic (even subclinical) uveitis. Boys tend to get sacroiliitis and are HLA B27 positive, which is associated with acute uveitis…
• Polyarthritis (rheumatoid factor -ve) – 5+ joints affected during first 6 months. Tends not to be hips! 17% of all JIA. Severity is very variable.
• Polyarthritis (RF +ve) – 7% of all JIA. Symmetrical polyarthritis, nodules, and Rheumatoid factor IgM +ve at least twice, 3 months apart. Typically adolescent girls of 10yrs+. Prognosis is guarded as early joint damage often occurs.
• Systemic onset – SOJIA, 11% of all JIA. Can occur at any age, often pre-school but rarely in infancy. Males and females affected equally.
• Enthesitis related arthritis – inflammation of tendon insertions eg sternum, around knee (at 2,6 and 10 o’clock positions), tibial tubercle, achilles/plantar, tibialis anterior, flexor digitorum insertion in foot. Often dactylitis. Asymmetric, distal lower limbs large joints commonly affected, high risk of developing ankylosing spondylitis in early adulthood – spine rarely affected early on. BASMI score consists of 5 measurements of spinal mobility. The group also includes arthritis or enthesitis with at least two of:
  • tenderness of the sacroiliac joint and/ or inflammatory spinal pain
  • HLA B27 positive (10% of normal population)
  • family history in a first or second degree relative of HLA B27 related disease (ie arthritis, IBD, Reiter’s, uveitis)
  • anterior uveitis (usually symptomatic with redness, pain and blurred vision)
  • arthritis after 8 years of age in a boy (esp large lower limb joints).
• Psoriatic arthritis – esp umbilicus, behind ear, scalp. The arthritis is usually asymmetrical, mixed large/small joints. Often NOT psoriasis, at least initially, but includes children with arthritis and at least two of:
  • dactylitis (fat, sore fingers!)
  • pitting or onycholysis of nails
  • psoriasis in a first degree relative
• Other arthritis – This group is for children with idiopathic arthritis that does not fit the other groups (or into more than one! eg Crohns & UC associated arthritis, features overlap). Downs syndrome children can get a resistant polyarthritis.

Presentation

Clinically, history of pain, swelling, stiffness. Pain is usually not severe, and often avoided completely by adapting movement; can occur at night, and occurs in the joint line. Degree of pain does NOT predict severity of synovitis. Swelling may be due to effusion or bony overgrowth. Stiffness not so severe as to cause gelling ie sitting still leads to freezing (cf myasthenia gravis, hypermobility). Bony overgrowth, discrepant leg length (longer with inflammation! Leads to postural scoliosis), wasting show chronicity.

Differentials:

• Benign hypermobility – typically get pain related to exertion, short lasting although may occur at night.
• Reactive arthritis – can last up to 3/12.
• Rubella, chronic meningococcus
• HSP before rash develops
• Rheumatic fever
• Behçets – mouth/genital ulcers, uveitis.
• SLE (high ESR with normal CRP, low WCC/platelets, autoantibodies) or dermatomyositis (stiffness, rather than true arthritis – proximal muscle weakness, high CK)

Investigations:

• Mono JIA usually CRP <7 – else beware infection
• Micro of joint fluid nonspecific
• XR – to exclude tumour etc. Lucency in metaphysis may be marrow infiltration in leukaemia, Brodie’s abscess or Langerhans’ histiocytosis. Moth eaten appearance and onion skin periosteal reaction suggests tumour or infection.
• RF v non specific, like autoantibodies, only significant in discriminating teenage girls with adult type Rheumatoid Arthritis.
• US is good but operator dependent. MRI probably better, predicts extension in mono, 4-11/12 before clinical signs.

Treatment

NSAIDs and intra-articular steroids work quickly. Ibuprofen can be given at high dose (10mg/kg qds), else Diclofenac 3-5mg/kg in 3-4 divided doses, max 150mg. Piroxicam is once daily, which is convenient but it probably has more GI/cutaneous side effects. No longer considered appropriate for acute pain.

Routine NSAIDs are probably pointless; if you need regular anti-inflammatories, you should probably be on a disease modifying agent eg methotrexate.

Joint injections are given under general anaesthetic in young children or with entonox in older children. Lederspan (triamcinolone) 1mg/kg max 40mg used for big joint, 0.5mg/kg for wrist, TMJ. Knuckles will only take 0.1-0.2ml before they start to leak (which leads to subcut atrophy). Injecting multiple (eg >6) sites can result in Cushings for 3-6/12. Better to pulse methylpred? (Kennilog is another formulation, but seems to give more Cushings). Most patients tolerate injections well and have no loss of function immediately after; physio is usually started after 24hr. How often? Balance of steroid effects and uncontrolled joint disease…

Methotrexate Side effects: GI (nause, ulceration, diarrhoea), hepatotoxicity (reversible elevations of serum liver enzymes eg 3x upper limit normal common), Pulmonary (oedema, pleuritic pain, pulmonary fibrosis, interstitial pneumonitis), mood changes, Renal (haematuria, dysuria, renal failure) – plus usual chemo stuff ie bone marrow suppression.

BNFc

Methotrexate is the disease modifying drug of choice – early use helps to reduce joint damage and minimise the exposure to, and side effects of, corticosteroids. Well tolerated in most children but often causes nausea the day after administration (so usually given on Friday to avoid affecting school). Avoid alcohol, as potentiates risk of cirrhosis. Takes 6-8 weeks to become effective so cover interval with intravenous methylprednisolone. The theoretical risk of malignancy and infertility has not so far been borne out in long term outcome studies. Folic acid improves tolerability but not clear what regimen to use – BNF suggests 5mg once weekly or 1mg daily, theoretically it should not be given within 24 hours of the MTX [so once weekly sounds easier]. Methotrexate is given once a week at 10-25mg/m2 – can be oral but subcut route improves bioavailability at doses beyond 10mg/m2. Metojet has better shelf life (10 months). Regular blood tests to monitor inflammatory markers and side effects eg monthly for 6 months then 3 monthly thereafter. Not great for axial disease ie HLA B27.

Steroids are useful for treating acute flares. Methylprednisolone can be given once daily for 3/7 to control severe exacerbations, then once weekly thereafter (30mg/kg, max 1g). Don’t work well for axial disease though ie HLA B27 (although may be good for peripheral joints) – TNF blockade (ie etanercept or infliximab) effective.

Patients who are refractory to high dose parenteral methotrexate are considered for monoclonal antibodies such as Etanercept/infliximab (TNF antibody), autologous stem cell transplantation, or very high dose immunosuppression.

• Etanercept (Embrel) used to be twice weekly subcut injection but most now do once weekly 0.8mg/kg. £10 000pa.
• Infliximab is an infusion, given at 0, 2, 6 weeks then 8 weekly thereafter. Children usually start at 5mg/kg. If control not achieved, a higher dose could be used else the interval reduced. Patients should get a CXR and Mantoux before starting in view of the particular risk of mycobacterial disease.
• IV immunoglobulin has been used eg 2 doses on consecutive days monthly. Very expensive.
• Mycophenolate – related to azathioprine. Used for connective tissue disease. SE gastrointestinal, liver, bone marrow. 600mg/m2 BD

Calcium and vitamin D supplements are often given for bone health.

Patients on immunosuppressants should avoid live vaccines and beware of infection. If unwell enough to need antibiotics they should probably stop treatment temporarily. Varicella is a particular concern – if contact with chickenpox and non-immune, consider VZIG or oral aciclovir for prophylaxis, and early IV aciclovir treatment. See Greenbook.

Not clear when to wean… Many patients do well for a year or so before their condition begins to worsen, swapping to another agent often works, and swapping back is also a useful option.

Outcome

JIA is a not a benign disease and outcome is variable. At least a third of patients have ongoing active disease into adulthood and many have sequelae eg:

• joint damage requiring joint replacement
• short stature from chronic disease compounded by steroid toxicity
• localised growth problems (micrognathia or leg length inequality)
• visual loss from uveitis
• osteoporosis: one off DEXA scan not predictive of # (maybe better if serial scans?) so clinical. Minimize steroids; optimize exercise, nutrition, growth/puberty, calc/vitD/bisphosph

Bisphosphonates seem to be effective for increasing bone mass in JIA. Flu-like symptoms with first IV dose can be treated with paracetamol and tend not to recur.