bubble_chart Overview

Vitamin B₆ includes six interconvertible forms: pyridoxine, pyridoxamine, pyridoxal, and their respective 5-phosphate derivatives. Pyridoxal 5-phosphate is a crucial component of this group, acting as a coenzyme in enzyme systems involved in decarboxylation and transamination processes, and participating in the metabolism of amino acids, proteins, lipids, nucleic acids, and glycogen in the body. Deficiency can lead to spasms and peripheral neuropathy. Therefore, a deficiency in vitamin B₆ can result in abnormalities in generation and transformation as well as physiological aspects. Vitamin B₆ dependency syndrome is a congenital metabolic disorder caused by structural and functional defects in the enzyme kynureninase, with its activity reduced to only 1% of normal. In such cases, the requirement for vitamin B₆ is 5 to 10 times higher than that of normal children. Sometimes, due to the mother taking excessive doses of vitamin B₆ during pregnancy, the infant may still require a higher amount of vitamin B₆ after birth.

bubble_chart Clinical Manifestations

In infancy, the main symptoms of pyridoxine deficiency are generalized spasms, with other manifestations including peripheral neuritis, dermatitis, and anemia. Infants within 6 months of birth who are fed a diet deficient in vitamin B₆ may exhibit nervousness, increased excitability, and frequent generalized spasms, leading to depression, drowsiness, mental retardation, and loss of vibratory and positional senses. Gastrointestinal symptoms are also common. When treating subcutaneous node disease with isoniazid, peripheral neuropathy and sexually transmitted diseases (more common in adults) may occur, as well as skin and mucous membrane inflammation, such as seborrheic and desquamative dermatitis, stomatitis, glossitis, and conjunctivitis.

Vitamin B6 dependency syndrome is mostly a hereditary disorder.

bubble_chart Auxiliary Examination

(1) Tryptophan Test: After oral administration of tryptophan to the sick child, urine is collected to measure the excretion of xanthurenic acid. If the excretion is lower than normal, it is considered a positive reaction.

(2) McHenry's Test: After oral administration or injection of alanine to the sick child, blood is drawn to measure the concentration of urea. If the urea concentration is significantly higher than normal, it is considered a positive reaction.

Both of these positive tests have only reference value for diagnosis.

bubble_chart Diagnosis

In infancy, if there are unexplained convulsions, anemia, or chronic diarrhea, and conditions such as hypocalcemia, hypoglycemia, hyponatremia, and infectious diseases have been ruled out, vitamin B₆ deficiency or dependency should be considered. The cessation of seizures after an injection of 100mg of vitamin B₆ can serve as a diagnostic criterion. A tryptophan load test can confirm the diagnosis, as follows: oral administration of 50-100mg/kg of tryptophan solution (with a total dose not exceeding 2g per administration) may result in a large amount of xanthurenic acid in the urine of the affected child, which is not seen in normal individuals. However, this test may be negative in cases of vitamin B₆ dependency, with reduced serum and erythrocyte glutamic-oxaloacetic transaminase levels. Electroencephalogram (EEG) examination may show abnormal frequency and amplitude changes in waveforms.

bubble_chart Treatment Measures

For spasms caused by pyridoxine deficiency, a single intramuscular injection of vitamin B₆

100mg can control the condition, followed by dietary adjustments. If it is a vitamin B₆ dependency disorder, it is necessary to administer 2-10mg intramuscularly daily, or orally 10-100mg until recovery. For the treatment of certain diseases where the drug used is a vitamin B₆ antagonist, oral administration of B₆ at approximately 2mg/kg/day is required.

bubble_chart Prevention

Food should be balanced, and when consuming high-protein foods, vitamin B₆ should be added. For patients with subcutaneous nodules undergoing isoniazid treatment, neurological symptoms should be monitored, and if abnormalities occur, the dosage of isoniazid should be reduced, preferably with the addition of vitamin B6. The normal requirement for vitamin B₆ is 0.3-0.5mg/day for infants and 0.5-2mg/day for children.