A 22-month-old boy from a resource-limited rural community is brought because of progressive abdominal distension, irritability, and poor linear growth over the past 3 months. He was weaned early from breastfeeding after the birth of a younger sibling and has since been fed predominantly a carbohydrate-rich cereal-based diet with minimal intake of pulses, milk, or other protein sources. Examination reveals bilateral pitting pedal edema, sparse hypopigmented easily pluckable hair, patchy areas of hyperpigmented skin with desquamation, and hepatomegaly. His weight is between 60% and 80% of the expected value for age. Laboratory investigations demonstrate marked hypoalbuminemia with normal renal function and no proteinuria. Which of the following is the most likely diagnosis? A) Protein-energy malnutrition characterized predominantly by visceral protein deficiency with preserved subcutaneous fat B) Severe calorie deficiency resulting in marked wasting without edema due to adaptation to prolonged starvation C) Chronic copper toxicity leading to progressive hepatic fibrosis and portal hypertension D) Medium-vessel necrotizing vasculitis characterized by coronary artery aneurysms and mucocutaneous inflammation
Answer: A - Kwashiorkor (Protein-Energy Malnutrition with Predominant Visceral Protein Deficiency)
Why This Child Has Kwashiorkor - Feature by Feature
| Finding | Mechanism in Kwashiorkor |
|---|---|
| Early weaning onto carbohydrate-rich cereal diet | Classic precipitating cause ("kwashiorkor" in Ga language describes the illness of a child displaced by a new sibling's birth) |
| Bilateral pitting pedal edema | Hypoalbuminemia reduces plasma oncotic pressure - fluid shifts to interstitium |
| Hepatomegaly | Reduced apolipoprotein synthesis prevents lipid export from liver, causing fatty change (steatohepatitis) |
| Sparse, hypopigmented, easily pluckable hair | Protein deficiency disrupts keratin synthesis and melanin production |
| "Flaky paint" dermatosis (hyperpigmentation + desquamation) | Characteristic alternating zones of hyper/hypopigmentation with desquamation |
| Weight 60-80% of expected | Typical range for kwashiorkor - true tissue loss masked by fluid retention |
| Marked hypoalbuminemia | Severe visceral protein depletion - liver cannot synthesize adequate albumin |
| Normal renal function, no proteinuria | Rules out nephrotic syndrome as the cause of edema |
| Irritability, listlessness | Classical behavioral features from protein deprivation |
Why the Other Options Are Wrong
Key Distinguishing Concept: Kwashiorkor vs. Marasmus
"In kwashiorkor, unlike in marasmus, marked protein deprivation is associated with severe loss of the visceral protein compartment, and the resultant hypoalbuminemia gives rise to generalized or dependent edema... there is relative sparing of subcutaneous fat and muscle mass."
- Robbins & Kumar Basic Pathology
"Children with kwashiorkor have characteristic skin lesions with alternating zones of hyperpigmentation, desquamation, and hypopigmentation, giving a 'flaky paint' appearance. Hair changes include loss of color... and loss of firm attachment to the scalp."
- Robbins, Cotran & Kumar Pathologic Basis of Disease
A 19-day-old infant is admitted with progressive lethargy, recurrent non-bilious vomiting, poor weight gain, and reduced feeding. Pregnancy and delivery were uneventful. Examination reveals dehydration, hypotension, and generalized hyperpigmentation involving the areolae and external genital region. External genital examination demonstrates labioscrotal fusion with a single perineal opening. Laboratory investigations show: Serum sodium: 122 mEq/L Serum potassium: 6.8 mEq/L Blood glucose: 48 mg/dL Arterial pH: 7.29 Plasma renin activity is markedly elevated, while aldosterone and cortisol concentrations are reduced. Which of the following investigations would provide the most specific biochemical confirmation of the underlying enzymatic defect? A) Demonstration of an exaggerated cortisol response following cosyntropin administration B) Markedly elevated circulating 17-hydroxyprogesterone concentration measured before initiation of glucocorticoid therapy C) Increased urinary excretion of 17-ketosteroids as the preferred confirmatory diagnostic test in neonates D) Simultaneous estimation of plasma ACTH and cortisol demonstrating primary adrenal insufficiency
Answer: B - Markedly Elevated 17-Hydroxyprogesterone Concentration
Diagnosis: Classic Salt-Wasting 21-Hydroxylase Deficiency (CAH)
Decoding the Clinical Features
| Finding | Pathophysiological Basis |
|---|---|
| Hyponatremia (Na 122), Hyperkalemia (K 6.8) | Aldosterone deficiency - no mineralocorticoid action on distal tubule |
| Hypotension, dehydration | Salt and water wasting |
| Hypoglycemia (glucose 48) | Cortisol deficiency - impaired gluconeogenesis |
| Metabolic acidosis (pH 7.29) | Aldosterone deficiency causes type IV RTA-like picture |
| Generalized hyperpigmentation | Elevated ACTH (loss of cortisol negative feedback) stimulates melanocortin receptors |
| Labioscrotal fusion, single perineal opening | 46,XX infant virilized in utero by androgen excess (ambiguous genitalia) |
| Markedly elevated PRA, low aldosterone and cortisol | 21-hydroxylase block prevents synthesis of both cortisol and aldosterone |
| Vomiting, lethargy, poor feeding at ~2-3 weeks | Classic timing of salt-wasting crisis presentation |
Why 17-Hydroxyprogesterone (17-OHP) is the Most Specific Test
- 17-OHP → 11-deoxycortisol (cortisol pathway)
- Progesterone → 11-deoxycorticosterone (aldosterone pathway)
"Diagnosis of 21-hydroxylase deficiency is made in infants and children with elevated concentrations of plasma 17-hydroxyprogesterone and androstenedione... Elevation of 17-hydroxyprogesterone concentrations in early infancy (>3000 ng/dL; 90.9 nmol/L) confirms the diagnosis of this disorder."
"A very high concentration of 17-hydroxyprogesterone in a randomly timed blood sample is diagnostic of classic 21-hydroxylase deficiency. Typically, salt-wasting patients have higher 17-hydroxyprogesterone concentrations than non-salt losers."
Why the Other Options Are Incorrect
- Immature renal function alters excretion rates
- 17-ketosteroids reflect androgen metabolites, not the specific 21-hydroxylase block
- Plasma 17-OHP is faster, more specific, and validated for neonatal diagnosis including dried blood spot screening