Arthritis in Children

Essentials

• Swelling and pain on motion in a single joint, fever above 38.5°C and CRP concentration above 20 mg/l suggest bacterial arthritis. In suspicion of such, a paediatric patient is referred on an emergency basis to a hospital for the consideration of an arthrocentesis performed under general anaesthesia.
• Aseptic arthritides are more common than septic ones. Their development is slower and the symptoms are milder and more difficult to recognize.
• In non-emergency situations, the primary laboratory tests include basic blood count with platelet count, CRP, ESR, streptococcal throat culture and chemical urinalysis.
• It is advisable to start symptomatic treatment with an NSAID without much hesitation.

Urgency of the diagnosis

1. Bacterial infections are managed on an emergency basis. Joint swelling and pain on motion, fever above 38.5°C and plasma CRP concentration above 20 mg/l in monoarthritis suggest a bacterial infection Osteomyelitis and Septic Arthritis in Children. In suspected cases, refer the child immediately to a hospital that has readiness to perform the necessary diagnostic procedures and to start treatment.
2. Aseptic arthritides that have an acute onset but are usually afebrile should preferably be diagnosed within 1-2 days. Inflammatory markers are only slightly increased at the most (table T1).
   • Transient synovitis of the hip (the diagnosis should be confirmed by ultrasonography) Hip Pain in Children
   • Henoch-Schönlein purpura Henoch-Schönlein Purpura
   • Urticaria with arthritis (serum sickness; often associated with antimicrobial treatment).
3. Slowly developing aseptic arthritides do not require accurate diagnostics on an emergency basis.
   • Transient arthritides probably associated with viral diseases
   • Juvenile idiopathic arthritis Juvenile Idiopathic Arthritis (Juvenile Rheumatoid Arthritis)
   • Other prolonged arthritides (poststreptococcal arthritis, Borrelia-related arthritis, enteroarthritis)

• If the symptoms have lasted for more than 2 weeks, determine antinuclear as well as Streptococcus (both ASO and anti-DNase B), Salmonella, Campylobacter, Yersinia and Borrelia antibodies.
• A delay of 2 weeks (during which time an NSAID is prescribed as needed) is a good "diagnostic test" because a significant number of arthritis cases are cured during that time and no further investigations are needed.

Investigations

• See table T1.
• See also article Articular status of a child with arthritic symptoms Articular Status of a Child with Arthritic Symptoms.

Differential diagnosis

• See also article Limp or refusal to walk in children Limp or Refusal to Walk in Children.
• In orthopaedic diseases of the hip Hip Pain in Children, knee Knee Complaints in Growing Children or ankle Painful Conditions of the Ankle and Foot in Children and Adolescents, the inflammatory markers are usually not increased and the pain is usually aggravated by strain. In inflammatory diseases, the pain - or rather the stiffness of the joint - is greatest after rest (morning stiffness).
• A normal blood leucocyte count does not rule out a septic infection but an increased count supports the diagnosis. The ESR rises more slowly than CRP but is better than CRP in the differentiation of any inflammatory condition from non-inflammatory (orthopaedic) causes of joint symptoms.
• Because leukaemia may initially manifest as joint symptoms (usually severe pain at night) the differential leucocyte count should be included in the initial investigations of arthritis.
• Beta-haemolytic group A streptococci may be detected in a throat smear in Henoch-Schönlein purpura Henoch-Schönlein Purpura and some other conditions that cause acute articular symptoms. In these cases, the streptococci should always be eradicated with antimicrobials. The possibility of rheumatic fever should be considered on the basis of the clinical presentation (fever and migratory polyarthritis, often erythema nodosum) if group A streptococci are detected. Poststreptococcal reactive arthritis is nowadays much more common than rheumatic fever.
• The urine test may be abnormal in Henoch-Schönlein purpura, systemic lupus erythematosus (haematuria), enteroarthritis (pyuria) and Kawasaki disease (pyuria).
• Remember the possibility of Kawasaki disease Kawasaki Disease if painful arthritis develops 1-2 weeks after an episode of high fever.
• Rheumatoid factor is rarely present in juvenile rheumatoid arthritis Juvenile Idiopathic Arthritis (Juvenile Rheumatoid Arthritis). It should not be included in the initial examinations of arthritis in children but rather postponed until further assessment and classification of prolonged arthritis is performed.

Urticaria and arthritis

• Urticaria and arthritis is a serum sickness-like disease usually caused by drugs. The presenting symptoms include
  • urticarial (or sometimes maculopapular) rash (picture 1) and
  • polyarticular erythema, swelling and pain on motion. Typical sites are the dorsum of the foot (pictures 2 3) and the MTP joints.
• The patient may have mild fever and a slightly elevated ESR; serum CRP concentration is increased more rarely.
• The symptoms commence suddenly after a course of antimicrobials and disappear in a week.
• Most common in children under school age
• Stop the medication (and avoid it in the future), and relieve the itch with antihistamines, e.g. hydroxyzine 1-2 mg/kg/day, if needed. Straining of the painful joints should be avoided.

Enteroarthritis

• An enterobacterial infection (yersiniosis, salmonellosis, campylobacter infection) is occasionally followed by severe arthritis that may be difficult to differentiate from septic arthritis. About 10% of children have joint symptoms after a salmonella infection.
• Typical clinical features of enteroarthritis are listed below.
  • The disease is polyarticular (which is exceptional in septic arthritis).
  • Children below school age are very rarely affected.
  • The large joints of the lower extremities (knees, ankles) are most commonly affected, but small joints of the toes and hands may also be affected.
  • The patient often has fever.
  • ESR, and plasma CRP concentrations may be considerably increased (> 50).

Borrelia arthritis

• A tick-bite or the erythema migrans skin eruption typical of Lyme borreliosis are recalled by a less than half of the patients.
• In Borrelia arthritis, serum anti-Borrelia IgG antibodies are clearly increased. See Lyme borreliosis Lyme Borreliosis (LB) for more details.
• Usually no fever; inflammatory markers moderately increased at the most
• Borrelia arthritis occurs throughout the year.

Poststreptococcal arthritis

• There is not necessarily a known history of a streptococcal infection with 4 weeks before the onset of the arthritis.
• Usually an acute-onset mono-, oligo- or polyarthritis with
  • positive throat culture for streptococci and/or
  • clearly increased serum concentrations of anti-streptococcal antibodies
    • Antistreptolysin at least > 600 U/ml (normally < 400) and/or
    • anti-DNase B at least > 400 U/ml (normally < 200)
• Fever is rare; inflammatory markers are moderately increased.
• Most common in school age children

Other acute forms of arthritis

• Many cases of acute arthritis that have a non-specific clinical presentation and that cannot be included in the aforementioned categories will be left without more specific diagnosis.
• Arthritis may be associated with viral infections (chickenpox, parvovirus, adenovirus).
• The determination of viral antibodies is seldom indicated because quick spontaneous recovery is the rule.

Treatment

• The treatment of an aseptic arthritis can always be started with an NSAID for e.g. 1-2 weeks (naproxen 10-20 mg/kg/day, diclofenac 1-3 mg/kg/day, ibuprofen 20-40 mg/kg/day).
• If the motion range of the joint has become restricted, a topical glucocorticoid injection is in most cases needed; the injection is administered at hospital (under anaesthesia).
• The treatment principles of poststreptococcal arthritis are not established. Because there is a (slight) possibility of carditis, the treatment is planned in specialized care, particularly concerning the long-term antimicrobial prophylaxis.
• For Borrelia arthritis, see Lyme borreliosis Lyme Borreliosis (LB).