Defisiensi Vitamin B2

01Pathophysiology

Riboflavin is a water-soluble vitamin absorbed primarily in the proximal small intestine. Once absorbed, it is phosphorylated intracellularly to form FMN (by flavokinase) and subsequently converted to FAD (by FAD synthetase). These two coenzymes are essential for a wide range of oxidation-reduction reactions throughout the body, including the electron transport chain (complexes I and II), fatty acid beta-oxidation, and the conversion of other B vitamins into their active forms.

FAD is required for the activity of methylenetetrahydrofolate reductase (MTHFR), which links riboflavin to folate metabolism. It is also required for the conversion of pyridoxine (B6) to its active coenzyme form, pyridoxal phosphate (PLP). This is why riboflavin deficiency rarely occurs in isolation and frequently presents alongside deficiencies of folate, niacin (B3), and pyridoxine (B6). This interdependence is a frequently tested concept.

The mucocutaneous signs of ariboflavinosis arise because rapidly dividing epithelial tissues are highly dependent on FAD/FMN-driven energy metabolism. When these coenzymes are deficient, epithelial turnover at the oral commissures, tongue surface, and skin folds is impaired, leading to angular cheilitis, glossitis, and seborrheic-like dermatitis. The corneal vascularization occurs because riboflavin is critical for maintaining corneal avascularity through its role in antioxidant defense (FAD is a cofactor for glutathione reductase, which regenerates reduced glutathione). Without adequate glutathione cycling, oxidative damage triggers neovascularization of the cornea.

The anemia seen in riboflavin deficiency is typically normocytic and normochromic, resulting from impaired iron mobilization and utilization (FAD is required for ferritin iron release). However, because riboflavin deficiency impairs folate metabolism via MTHFR, a secondary megaloblastic component can develop if folate status is borderline.

02Classification and Clinical Manifestation

A key teaching point: the magenta or purplish hue of the tongue is what distinguishes riboflavin-related glossitis from the beefy red glossitis of B12/folate deficiency and the raw, scarlet glossitis of niacin deficiency (pellagra). This color distinction is a reliable discriminator in vignettes.

03Diagnostic Workup

The best initial test in clinical practice is often the clinical diagnosis itself, as the triad of angular cheilitis, glossitis, and dermatitis in a malnourished or alcoholic patient is strongly suggestive. However, when biochemical confirmation is needed, the EGRAC is the most reliable functional assay. It works by measuring the activity of glutathione reductase in red blood cells before and after the addition of exogenous FAD in vitro. If the enzyme activity increases substantially after FAD is added (coefficient > 1.4), it proves the enzyme was undersaturated with its cofactor, confirming tissue-level riboflavin deficiency.

Urinary riboflavin reflects short-term intake and drops quickly with inadequate diet, making it useful as a population-level screening tool but less reliable for individual diagnosis.

Because riboflavin deficiency impairs the metabolism of folate, B6, and niacin, a complete B-vitamin assessment should be ordered. Exam vignettes may present a patient who appears to have pellagra or B6 deficiency but fails to respond to targeted supplementation, and the "next best step" is to check riboflavin status and supplement accordingly.

04Management and Treatment

Oral supplementation is the mainstay of treatment. Riboflavin is well absorbed even in moderate malabsorption states because absorption occurs via a saturable, carrier-mediated transport system in the proximal jejunum. Doses above approximately 25 to 30 mg are absorbed with diminishing efficiency, so dividing larger doses (e.g., 10 mg three times daily rather than 30 mg once daily) improves bioavailability.

Clinical improvement is usually rapid. Angular cheilitis and glossitis begin improving within days to one to two weeks, while corneal vascularization may take longer to regress. Patients should be counseled that their urine may turn bright yellow/fluorescent during supplementation, which is a harmless sign of riboflavin excretion and not a cause for concern.

An important management pearl: if a patient with suspected pellagra (niacin deficiency) does not improve with niacin supplementation alone, consider underlying riboflavin deficiency. FAD is required for the tryptophan-to-niacin conversion pathway (the enzyme kynurenine 3-monooxygenase is FAD-dependent), so riboflavin deficiency can functionally cause secondary niacin deficiency. The "next best step" in a niacin-refractory pellagra case is to add riboflavin.

There are no notable drug contraindications to riboflavin supplementation. It is safe in pregnancy and in patients with renal or hepatic impairment. Excess riboflavin is efficiently excreted in urine, making toxicity essentially nonexistent.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students miss riboflavin deficiency questions is by anchoring on a single mucocutaneous finding (like angular cheilitis or glossitis) and jumping to iron deficiency or B12 deficiency without considering the full clinical picture. The exam tests whether you can recognize the combination of oral, ocular, and genital findings as a unified syndrome rather than isolated problems.

A second frequent trap involves the interdependence of B vitamins. A vignette may describe a malnourished patient treated for pellagra or B6 deficiency who fails to improve. The expected next step is not to increase the dose of the current supplement but to add riboflavin, because FAD is upstream of both the niacin synthesis pathway and the B6 activation pathway. Students who do not understand this metabolic relationship will miss the question.

The magenta tongue is the single most reliable vignette cue. While many B-vitamin deficiencies cause glossitis, the purplish-magenta color is distinctive to riboflavin deficiency, as opposed to the beefy red tongue of B12/folate deficiency or the scarlet tongue of pellagra. If a question stem uses the word "magenta" in any context, riboflavin should immediately be at the top of your differential.

Finally, remember that corneal vascularization in the context of nutritional deficiency points almost exclusively to riboflavin. This finding is uncommon in other vitamin deficiencies and serves as a strong discriminator when the oral findings are ambiguous.

The core competency being tested is the ability to (1) recognize the oro-oculo-genital triad, (2) understand the metabolic role of FAD/FMN as upstream cofactors for other B-vitamin pathways, and (3) identify riboflavin deficiency as the underlying cause when targeted B-vitamin supplementation for another deficiency fails to produce clinical improvement.