Differential Diagnosis for Multiple Bowing of Limbs with Features of Rickets

Single Most Likely Diagnosis

• Vitamin D Deficiency Rickets: This condition is characterized by softening of the bones due to a lack of vitamin D, leading to bowing of the limbs, among other symptoms. The very low vitamin level in a 6-year-old who was previously walking but has since stopped, strongly suggests a nutritional deficiency affecting bone health.

Other Likely Diagnoses

• Hypophosphatemic Rickets: A condition where the bones become soft due to a lack of phosphate, which can also lead to bowing of the limbs and is often associated with vitamin D deficiency.
• Renal Rickets: Caused by kidney problems that affect the body's ability to regulate phosphate and calcium levels, leading to softening of the bones.
• Vitamin D-Dependent Rickets Type 1: A rare genetic disorder affecting the enzyme responsible for converting vitamin D into its active form, leading to rickets despite adequate vitamin D intake.

Do Not Miss Diagnoses

• Hypoparathyroidism: A condition where the parathyroid glands are underactive, leading to low calcium levels, which can cause muscle cramps, spasms, and tetany, and if untreated, can lead to more severe complications including seizures and heart problems.
• Pseudovitamin D-Deficiency Rickets (Vitamin D-Dependent Rickets Type 2): A rare condition where the body is resistant to vitamin D, requiring very high doses of vitamin D and calcium to treat.

Rare Diagnoses

• Achondroplasia: The most common form of short-limbed dwarfism, which can present with bowing of the limbs but is primarily a genetic disorder affecting bone growth.
• Fibrous Dysplasia: A condition where normal bone and marrow are replaced with fibrous tissue, leading to weak bones and potential deformities, including bowing of the limbs.
• Osteogenesis Imperfecta: A genetic disorder characterized by fragile bones, often presenting with fractures and bowing of the limbs, but typically associated with blue sclerae and hearing loss.

Treatment for the most likely diagnosis, Vitamin D Deficiency Rickets, involves supplementation with vitamin D and calcium, along with monitoring of serum levels to ensure they return to normal. Physical therapy may also be necessary to help the child regain the ability to walk. For other diagnoses, treatment varies and may include specific medications, dietary changes, or in some cases, surgical intervention.