Failure to Thrive in a 9-Month-Old
A 9-month-old girl is brought to your clinic for a well-child visit. Her weight is 6.8 kg (below the 3rd percentile, down from the 25th percentile at 6 months), length is 68 cm (10th percentile), and head circumference is 43 cm (25th percentile). The mother reports the infant is breastfed on demand and has just started purees. She seems satisfied after feeds but feeds frequently at night. The infant is alert, interactive, and has normal tone. No dysmorphic features. The mother is a 22-year-old single parent with limited support and reports food insecurity. The clinic has a lactation consultant available weekly and a social worker.
1. What is the differential diagnosis for this infant's poor weight gain, and what key history and exam findings would you seek?
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Differential includes: inadequate caloric intake (breastfeeding difficulties, low milk supply, improper formula mixing, food insecurity), malabsorption (celiac disease, cystic fibrosis, cow's milk protein allergy), increased metabolic demand (chronic infection, congenital heart disease, hyperthyroidism), and psychosocial factors (neglect, maternal depression, poverty). Key history: detailed feeding diary (frequency, duration, volume, formula preparation), stool pattern (frequency, consistency, malodorous), urine output, developmental milestones, and maternal mental health. Exam: assess for signs of dehydration, wasting, organomegaly, and developmental delay. The infant's normal interactivity and tone suggest that severe chronic illness is less likely, but growth faltering is significant.
2. What initial management steps and referrals are appropriate, and how would you monitor progress?
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Initial steps: lactation consultation to assess breastfeeding technique and milk transfer, and to consider supplementation with expressed breast milk or formula. Social work referral to address food insecurity and support. Nutritional counseling with a dietitian. Laboratory screening: CBC, CMP, celiac screen, and possibly sweat chloride if malabsorption suspected. Close follow-up in 1-2 weeks with weight check. If weight gain remains inadequate, consider further evaluation (e.g., endocrine, GI). Monitor weight, length, and head circumference at each visit; a sustained drop in weight-for-length percentile warrants escalation. Document a clear plan and involve the mother in shared decision-making.