J Korean Endocr Soc.  2009 Sep;24(3):212-216. 10.3803/jkes.2009.24.3.212.

A Case of Osteomalacia with Multiple Fractures and Hypocalcemia Associated with Phenytoin Therapy

• Kim EK
• Lee MS
• Chung YS
• Kwack KS
• Hong JM
• Won YY

• KMID: 2178185
• DOI: http://doi.org/10.3803/jkes.2009.24.3.212

Abstract

Many studies have shown that patients taking antiepileptic drugs are at an increased risk for metabolic bone disease and low bone mineral density. Traditionally, this has been attributed to alterations in vitamin D metabolism by antiepileptic drugs which induce hepatic microsomal cytochrome P450 enzyme. However, there appear to be multiple mechanisms for antiepileptic drug-induced bone loss including lack of physical activity, reduced sunlight exposure, increased propensity for falling, and fractures associated with seizures or loss of consciousness. We experienced a case of antiepileptic drug-induced osteomalacia in a 63-year-old woman who had been on phenytoin for 8 years and was admitted with hypocalcemic seizures and multiple pathological fractures. This patient also had other risk factors for osteomalacia including reduced sunlight exposure, prolonged immobilization, and decreased dietary vitamin D intake. We discontinued phenytoin, and started calcium and vitamin D replacement. The patient's serum calcium and vitamin D level were normalized after treatment. Metabolic bone disease including osteomalacia should be considered in patients who are taking antiepileptic drugs especially those who are exposed to other risk factors.

Keyword

antiepileptic drugs; osteomalacia; phenytoin

MeSH Terms

Anticonvulsants
Bone Density
Bone Diseases, Metabolic
Calcium
Cytochrome P-450 Enzyme System
Female
Fractures, Spontaneous
Humans
Hypocalcemia
Immobilization
Middle Aged
Motor Activity
Osteomalacia
Phenytoin
Risk Factors
Seizures
Sunlight
Unconsciousness
Vitamin D
Anticonvulsants
Calcium
Cytochrome P-450 Enzyme System
Phenytoin
Vitamin D

Figure

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  Fig. 1 Plain radiography revealed thinning of cortices and fracture of right distal femoral shaft with cast application state.

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  Fig. 2 Increased uptakes in right distal femur, left proximal femur and distal tibia (arrows) were observed in whole body bone scan suggesting recent or unhealed fractures. Multiple focal increased uptake in both ribs showing multiple rib fractures and metabolic bone diseases.

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  Fig. 3 Bone mineral densitometry revealed severely decreased bone mineral density of lumbar (L1~4) vertebrae.

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