Water-Soluble Vitamin Deficiencies in Children
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Direct answer
Water-soluble vitamin deficiencies in children mainly involve thiamine, niacin, riboflavin and pyridoxine, and each has a classic signature. Infantile beriberi, from thiamine deficiency in a breastfed infant of a deficient mother, presents with aphonia and high-output heart failure. Pellagra and riboflavin deficiency cause dermatitis and mucosal lesions, while pyridoxine-responsive neonatal seizures are treated with intravenous pyridoxine.
What you must remember
- Thiamine: infantile beriberi occurs at about two to six months in breastfed infants, with aphonia, vomiting, tachycardia and high-output cardiac failure.
- Niacin: pellagra presents with the three Ds of dermatitis, diarrhoea and dementia, typically in maize-based diets low in tryptophan.
- Riboflavin: cheilosis, angular stomatitis, glossitis, seborrhoeic dermatitis and corneal vascularisation are the classic features.
- Pyridoxine-dependent epilepsy: neonatal seizures that respond to intravenous pyridoxine, commonly 100 mg, serve as both a diagnostic and therapeutic test.
- Isoniazid: interferes with pyridoxine metabolism, causing peripheral neuropathy, so pyridoxine is routinely added during tuberculosis treatment.
- Treatment principle: in a malnourished child with unexplained encephalopathy, thiamine is given before glucose to avoid precipitating Wernicke encephalopathy.
- Doses: parenteral thiamine for beriberi, oral nicotinamide for pellagra and commonly 10 mg daily pyridoxine with isoniazid are standard starting points.
- Assessment: a detailed diet history and the drug list usually reveal the cause; exclusively breastfed infants of vegan mothers also develop B12-deficiency megaloblastic anaemia and tremors, and scurvy causes gum bleeding and pseudoparalysis.
Matching the vitamin to its presentation
Each deficiency has a signature presentation, and the table links the vitamin to its classic picture and first-line response. Thiamine and niacin deficiencies are most often linked to diet, while pyridoxine problems are most often linked to drugs and inherited seizure disorders.
| Vitamin | Classic presentation | Key treatment point |
|---|---|---|
| Thiamine (B1) | Infantile beriberi: aphonia, vomiting, tachycardia, heart failure | Parenteral thiamine, then oral, with cardiac support |
| Niacin (B3) | Pellagra: photosensitive dermatitis, diarrhoea, dementia | Oral nicotinamide and dietary correction |
| Riboflavin (B2) | Cheilosis, glossitis, angular stomatitis | Oral riboflavin with a varied diet |
| Pyridoxine (B6) | Neonatal seizures, or neuropathy with isoniazid | Intravenous for seizures, daily with isoniazid |
| Vitamin C | Scurvy: gum bleeding, bone pain, refusal to walk, perifollicular haemorrhage | Oral vitamin C, with diet correction |
A breastfed infant with aphonia and tachycardia should prompt a thiamine trial before a cardiac cause is pursued. Maize-based diets and isoniazid therapy are the exposures examiners expect you to link.
Where the exam tries to catch you
Vitamin questions often hinge on the trigger, such as a diet type or a drug, rather than on the disease name.
- Trap: diagnosing neonatal seizures as idiopathic without a pyridoxine trial. Correct: pyridoxine-responsive seizures are treated with intravenous pyridoxine, which is both diagnostic and therapeutic.
- Trap: giving glucose to an encephalopathic malnourished child before thiamine. Correct: thiamine should precede glucose to prevent precipitating Wernicke encephalopathy.
- Trap: treating aphonia in a breastfed infant as a laryngeal problem. Correct: aphonia with tachycardia and vomiting points to infantile beriberi, and thiamine is the treatment.
Frequently asked questions
Which vitamin deficiency causes aphonia and cardiac failure in breastfed infants?
Thiamine deficiency causes infantile beriberi in breastfed infants, usually between two and six months of age. Aphonia, vomiting and tachycardia with high-output cardiac failure are the classic signs, and parenteral thiamine is the treatment.
Why is pyridoxine given alongside isoniazid in tuberculosis treatment?
Isoniazid interferes with pyridoxine metabolism and can cause peripheral neuropathy. Pyridoxine supplementation, commonly 10 mg daily, is added to isoniazid to prevent this neuropathy, especially in malnourished children.
What is the classic triad of pellagra?
The classic triad of pellagra is dermatitis, diarrhoea and dementia, and untreated pellagra can end in death. Pellagra arises from niacin deficiency, often in maize-based diets low in tryptophan.
How is a neonate with pyridoxine-responsive seizures treated?
Neonates with pyridoxine-responsive seizures are treated with intravenous pyridoxine, commonly 100 mg. Because the response confirms the diagnosis, a seizure that persists despite standard anticonvulsants should prompt a pyridoxine trial under specialist guidance.