Table 1.

Selected differential diagnosis for acute limp pain or pseudoparalysis

Differential diagnosis of acute focal pain in limb or near bone	Predominant symptoms	Other differentiating features
Acute bacterial osteoarticular infection (AO)	Acute onset of new limp, reluctance to use a limb or pseudoparalysis in a preverbal child. With spinal infection, reluctance to sit or stand or an impaired ability to bend due to pain may be present. Possible fever or rigours in the days before presentation.	Localized pain to palpation or point tenderness with pressure, overwhelmingly at the distal or proximal ends of bones. May be unable to move joint actively with adjacent SA. Usually accompanied by mild, localized swelling and (sometimes) by erythema. Localized fluctuance may be present if there is a periosteal abscess. Usually, child has had fever but may not be prominent at time of presentation.
Transient synovitis of hip	Usual age is 4–10 years. Hip pain and new limping, fever generally low-grade. Child can usually weight-bear but also may not. History of upper respiratory tract infection in the preceding 2 weeks.	Nontoxic appearance, usually < 38.5°C fever. CRP is usually < 20 mg/L. Gradually improves over several days, which may be hastened by nonsteroidal anti- inflammatory agents.
Fracture or trauma (e.g., Toddler’s fracture)	Acute onset of pain while active or after a recognizable traumatic event.	Localized pain to palpation. Hematoma or bruising, with localized swelling if trauma is local. No history of fever.
Lyme disease arthritis	Living in or travel to a Lyme-endemic area 2 to 12 months before symptom-onset. Usually monoarthritis, with swelling of a knee (occasionally hip or other large joints) without major constitutional symptoms on history.	Much less painful than SA. Usually, child does not have recent fever. Baker’s cyst may be present. Often still willing to weight-bear. CRP is < 40 mg/L.
Cellulitis	Rapid development of swelling, redness and pain over hours or a day. Erythema has usually preceded the development of pain.	Area of erythema, warmth, swelling and tenderness of the skin. Usually is more extensive than one focal area. Skin is edematous and tender to touch. Can have lymphangitis. Child may be able to weight-bear and move an underlying joint.
Chronic recurrent multifocal osteomyelitis (CRMO) (first presentation)	Insidious onset of bone pain. Lesions often affect the metaphysis and the epiphysis. Child may have low-grade fever and malaise. Pain is often worse at night. Diagnosis is based on a relapsing disease course. Lesions often involve unusual sites, such as the clavicle, jaw or scapula. There may be intense sclerosis with healing on radiographs.	Local tenderness with some warmth and swelling but sometimes no objective signs. One-third of cases have low-grade fever, malaise and weight loss. May have palmoplantar pustulosis, psoriasis or other dermatologic conditions.
Hematologic malignancy	Prominent associated systemic complaints, such as fever, fatigue, anorexia, weight loss and arthralgia, limb or muscle pain. Child may be reluctant to walk or have metaphyseal lucencies and periosteal reactions, as with acute osteomyelitis.	No localized pain to palpation but may have joint swelling and evidence of mild synovitis on joint exam. May have fever.
Bone neoplastic lesion (benign or malignant, including histiocytosis)	Typically occurs in the diaphysis or in flat bones. Typically gradual onset (over weeks).Pain is often worse at night and associated with refusal to weight-bear.	In addition to pain, may have a palpable soft tissue or bony mass.
Juvenile idiopathic arthritis	Typically gradual onset (over weeks). May be oligoarthritic (<4 joints) or polyarthritic. More likely to be symmetric, often with extra- articular symptoms.	Often, symptoms are less severe compared with bacterial SA. May have contracture if more subacute. May need synovial fluid analysis to exclude SA when presenting with monoarthritis. Usually, fewer white blood cells in joint fluid compared with SA.
Systemic lupus erythematosus	Often constitutional symptoms (fever, weight loss, fatigue, anorexia, diffuse lymphadenopathy) predominate. Cutaneous symptoms (e.g., rash, ulcers) at presentation are also common.	Arthritis is usually milder than with SA. Child may also have hematologic (leukopenia, anemia) abnormalities and abnormal urinalysis.
Reactive arthritis	Oligoarthritis of larger joints, usually 2 to 3 weeks after a preceeding infection of the gastrointestinal or urogenital tract. May also have ocular and urinary symptoms.	Arthritis is more subacute and less severe compared with bacterial SA.
Poststreptococcal reactive arthritis	Acute onset of symmetrical or asymmetrical arthritis. Usually polyarticular, nonmigratory and can be persistent or recurrent. Usually 3–14 days after preceding streptococcal infection.	May have extra-articular manifestations, (e.g., vasculitis, glomerulonephritis). In acute rheumatic fever, the joints are tender and swollen with a characteristic migratory feature and exquisite response to non-steroidal anti-inflammatory drugs or salicylates.

AO Acute osteomyelitis; CRP C-reactive protein; SA Septic arthritis.