What is the interpretation of a bone scan result that is 2 standard deviations away from the mean in a 14-year-old patient?

Bone Age Assessment in a 14.5-Year-Old with 2 Standard Deviations Delay

A bone age that is 2 standard deviations below chronological age (bone age approximately 12.6 years in a 14.5-year-old) indicates significant skeletal maturation delay that warrants thorough evaluation for underlying endocrine disorders, chronic systemic disease, or constitutional growth delay.

Understanding the Result

• Standard deviation interpretation: In pediatric bone age assessment, Z-scores (standard deviations from age-matched norms) should be used rather than T-scores, as T-scores compare to adult peak bone mass and are inappropriate for children 1
• Clinical significance: A 2 SD delay represents approximately 1.9 years of skeletal maturation delay (14.5 - 12.6 = 1.9 years), which falls well outside the normal variation range 1
• Body size considerations: Bone mineral density and skeletal maturation can be significantly influenced by height and weight deviations from age-matched peers, with nearly 1 in 5 children showing differences of more than 1 unit when body size is not accounted for 2

Differential Diagnosis to Consider

Endocrine causes (most common):

• Growth hormone deficiency
• Hypothyroidism
• Hypogonadism or delayed puberty
• Cushing syndrome (chronic glucocorticoid exposure)
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Chronic systemic diseases:

• Inflammatory bowel disease
• Celiac disease
• Chronic kidney disease
• Malnutrition or eating disorders
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Constitutional delay:

• Familial pattern of late maturation
• Often associated with delayed puberty
• Diagnosis of exclusion
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Required Clinical Evaluation

Essential history elements:

• Growth velocity over past 1-2 years (plot on growth chart)
• Pubertal development stage (Tanner staging)
• Family history of delayed growth/puberty
• Chronic illness symptoms
• Medication history (especially glucocorticoids)
• Nutritional assessment
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Laboratory workup indicated:

• Complete blood count, ESR/CRP
• Comprehensive metabolic panel
• Thyroid function tests (TSH, free T4)
• IGF-1 and IGFBP-3 (growth hormone axis)
• Celiac screening (tissue transglutaminase)
• Gonadotropins (LH, FSH) and sex hormones
• Bone age films of left hand/wrist for confirmation
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Management Approach

Immediate actions:

• Refer to pediatric endocrinology for comprehensive evaluation if not already done 1
• Document height velocity and plot on appropriate growth curves 2
• Assess for signs of underlying pathology requiring urgent intervention 1

Monitoring strategy:

• Repeat bone age assessment in 6-12 months to assess progression 1
• Serial height measurements every 3-6 months to calculate growth velocity 2
• Use same imaging facility and technique for accurate comparison, as measurement variability can be significant 3

Critical Pitfalls to Avoid

• Do not dismiss as "constitutional delay" without excluding pathologic causes through appropriate endocrine and systemic disease workup 1
• Avoid using T-scores in pediatric populations, as this leads to mislabeling children as "osteoporotic" when comparing to adult norms 1
• Account for body size deviations: Height and weight significantly influence bone density measurements, and failure to adjust can alter clinical management in nearly 20% of cases 2
• Recognize measurement limitations: Single measurements have inherent variability, and confidence intervals can be wide, particularly in those with low measured values 4
• Do not delay referral: A 2 SD delay represents clinically significant deviation requiring specialist evaluation, as delayed diagnosis of treatable conditions (hypothyroidism, growth hormone deficiency) can result in permanent height loss 1