What is the diagnosis and treatment for a 12-year-old girl with abdominal pain and leg pain?

Abdominal Pain and Achy Legs in a 12-Year-Old Girl

Begin with clinical risk stratification and targeted laboratory testing, followed by ultrasound as first-line imaging if appendicitis remains a concern, while simultaneously considering musculoskeletal causes for the leg pain.

Initial Clinical Assessment

The combination of abdominal pain with leg pain in a 12-year-old requires evaluation for both intra-abdominal pathology and musculoskeletal or systemic causes. 1

Key History and Physical Examination Elements

• Assess for alarm symptoms that indicate organic disease: fever, weight loss, gastrointestinal bleeding, persistent vomiting, chronic severe diarrhea, or blood in stool 2, 3
• Determine pain characteristics: Does the pain migrate from periumbilical to right lower quadrant (suggesting appendicitis, LR 1.9-3.1)? 4
• Evaluate the leg pain specifically: Nonspecific lower leg/foot pains are frequently underreported in pediatric patients and may be associated with pes planovalgus (flat feet), hypocalcemia, or juvenile idiopathic arthritis 5
• Check for fever: Fever is the single most useful sign for appendicitis (LR 3.4), while its absence decreases likelihood (LR 0.32) 4
• Perform abdominal examination: Look for rebound tenderness (LR 3.0 for appendicitis), right lower quadrant tenderness, guarding, or rigidity 6, 4
• Examine all hernia orifices and surgical scars, as this critical step is frequently overlooked 1

Laboratory Workup

Obtain the following initial tests: 7, 8

• Complete blood count: Leukocytosis suggests infection or inflammation; WBC <10,000/μL decreases appendicitis likelihood (LR 0.22) 7, 4
• Comprehensive metabolic panel: Assess for electrolyte abnormalities and organ function 7
• Serum calcium and magnesium: Hypocalcemia can cause cramping leg pain 5
• Urinalysis: Rule out urinary tract infection or nephrolithiasis 7
• Beta-hCG: Mandatory in all females of reproductive age to exclude pregnancy-related conditions 7, 8
• Consider inflammatory markers (ESR, CRP): Elevated levels may suggest inflammatory conditions like juvenile idiopathic arthritis 5, 3

Imaging Algorithm

If appendicitis remains a diagnostic consideration after clinical assessment: 1

• Ultrasound of the right lower quadrant is first-line imaging (86% sensitivity, 97% specificity), avoiding radiation exposure and identifying alternative diagnoses like ovarian pathology 1
• Do NOT obtain plain radiographs as primary imaging—they are neither sensitive nor specific for appendicitis 1
• If ultrasound is equivocal or nondiagnostic, proceed to CT abdomen/pelvis with IV contrast (>90% sensitivity and specificity) or consider MRI to avoid radiation 1

For musculoskeletal evaluation if leg pain predominates:

• Consider plain radiographs of affected areas if specific bony pathology is suspected 5
• Scoliosis screening is recommended in this age group, as adolescent idiopathic scoliosis is common and may cause pain 5

Differential Diagnosis Considerations

Abdominal Pain Causes

• Appendicitis: Most common surgical cause in children 6
• Gastroenteritis: Most common medical cause 6
• Constipation: Common functional cause 1
• Ovarian pathology: Ovarian torsion or cysts in females 1
• Functional abdominal pain: Diagnosis of exclusion when no organic cause found 2, 3

Leg Pain Causes

• Musculoskeletal: Pes planovalgus, growing pains, or overuse 5
• Hypocalcemia: Can cause cramping leg pain 5
• Juvenile idiopathic arthritis: Often polyarticular, may be associated with IgA deficiency 5
• Referred pain: Consider systemic illness like tuberculosis if constitutional symptoms present (fever, weight loss, night sweats) 9

Management Approach

If appendicitis is suspected (high clinical suspicion):

• Proceed to surgical consultation for potential appendectomy 1, 6
• Broad-spectrum antibiotics are NOT routinely indicated unless complicated appendicitis is confirmed 1

If functional abdominal pain is diagnosed:

• Focus on improving quality of life rather than complete pain resolution 3
• Consider psychological therapies: Cognitive behavioral therapy and hypnotherapy have demonstrated benefit 3
• Reassure parents and child about the benign nature of the condition 3

For leg pain management:

• Consider orthotics if pes planovalgus is present 5
• Correct hypocalcemia if identified 5
• Refer to rheumatology if juvenile idiopathic arthritis is suspected 5

Critical Pitfalls to Avoid

• Do not assume negative ultrasound rules out all pathology—if clinical suspicion remains high, proceed to CT or MRI rather than discharging 1
• Do not use CT as first-line imaging in pediatric patients—always attempt ultrasound first to avoid radiation exposure 1
• Do not overlook pregnancy testing in females of reproductive age before imaging 7, 8
• Do not dismiss leg pain as unrelated—consider systemic causes that may present with both abdominal and musculoskeletal symptoms 5, 9
• Do not perform extensive workup for functional pain—this is a clinical diagnosis requiring no testing if alarm symptoms are absent 2, 3