Scurvy Workup

Laboratory tests are usually not helpful to ascertain a diagnosis of scurvy. Presentation of an infant with the typical clinical and radiologic picture of scurvy, along with a supportive history of dietary deficiency of vitamin C, is often sufficient to diagnose infantile scurvy.

Plasma ascorbic acid level may help in establishing the diagnosis, but this level tends to reflect the recent dietary intake rather than the actual tissue levels of vitamin C. Signs of scurvy can occur with low-normal serum levels of vitamin C.

The best confirmation of the diagnosis of scurvy is remains its resolution following vitamin C administration.

Noninflammatory perivascular extravasation of red cells and deposition of hemosiderin near hair follicles with intrafollicular keratotic plugs and coiled hair may be seen in a skin biopsy specimen.

Obtaining a plasma or leukocyte vitamin C level can confirm clinical diagnosis.

Plasma levels

A fasting serum ascorbic acid level greater than 0.6 mg/dL rules out scurvy. Serum ascorbic acid levels of less than 0.2 mg/dL are deficient. levels of 0.2-0.29 mg/dL are low, and levels greater than 0.3 mg/dL are acceptable. Scurvy generally occurs at levels less than 0.1 mg/dL.^[17]

Leukocyte levels

The level of vitamin C in leukocytes more accurately correlates to tissue stores compared with serum levels, because these cells are not affected acutely by circadian rhythm or dietary changes. A level of zero indicates latent scurvy. levels greater than 15 mg/dL reflect a state of nutritional adequacy. levels of 8-15 mg/dL are considered low. levels of 0-7 mg/dL reflect a state of deficiency.

A specific and reproducible reverse-phase, high-pressure liquid chromatographic method has been found reliably to measure vitamin C in lymphocytes.^[18] This test is currently not clinically available, but it might be useful for screening.

Urinary levels

A more commonly used method is the ascorbic acid tolerance test, which quantitates urinary ascorbic acid over the 6 hours following an oral load of 1 g of ascorbic acid in water.

Radiographic findings in infantile scurvy are diagnostic and may show any of the following:

• Subperiosteal elevation
• Fractures and dislocation
• Alveolar bone reabsorption
• Ground-glass appearance of cortex, as in the image below.Anteroposterior radiograph of the lower extremities shows ground-glass osteopenia, a characteristic of scurvy.

The earliest radiologic manifestation of infantile scurvy is generally seen at the distal ends of the radii where fuzziness of the lateral aspects of the cortices is present with slight rarefaction of the neighboring cancellous bone. The characteristic radiologic changes occur at the growth cartilage-shaft junction of bones with rapid growth. The knee joint, wrist, and sternal ends of the ribs are typical sites of involvement.

As the disease progresses, radiographs demonstrate characteristic changes at the cartilage-shaft junctions of the long bones, especially at the distal ends of the femurs. Key imaging features show osteoporosis. The cortex becomes thin and the trabecular structure of the medulla atrophies and develops a ground-glass appearance. The zone of provisional calcification becomes dense and widened, and this zone is referred to as the white line of Fränkel. The epiphysis also shows cortical thinning and the ground-glass appearance.

Metaphyseal spurs or marginal fractures (Pelkan spur), a transverse band of radiolucency in the metaphysis (scurvy line or Trümmerfeld zone), which is subjacent to the zone of provisional calcification; ring of increased density surrounding the epiphysis (Wimberger ring); and periosteal elevation can also be noted.

As scurvy becomes advanced, a zone of rarefaction occurs at the metaphysis under the white line. The zone of rarefaction typically involves the lateral aspects of the white line, resulting in triangular defects called the corner sign of Park. This area has multiple microscopic fractures and may collapse with impaction of the calcified cartilage onto the shaft. The lateral aspect of the calcified cartilage can project as a spur. Subperiosteal hemorrhages are not visualized in the active phase. With healing, they become calcified and are readily observed.