History and exam
Key diagnostic factors
uncommon
features of chronic kidney disease
features of underlying malabsorption syndrome
Malabsorption (which may lead to vitamin D deficiency and poor calcium absorption) may arise from a number of conditions, such as Crohn disease, celiac disease, chronic pancreatitis or Whipple disease, or following gastric bypass surgery.[15] Frequently these diagnoses have already been established. Patients often have a history of long-standing gastrointestinal symptoms such as abdominal pains, irregular bowel habit, and chronic diarrhea.
Other diagnostic factors
common
muscle cramps and bone pain
These are common symptoms of SHPT and/or osteomalacia.
A possible explanation of the pain in patients with vitamin D deficiency is that the poorly mineralized osteoid becomes hydrated and cannot provide sufficient support for the sensory fibers in the periosteum.[16] The pain commonly affects the pelvis, hips, legs, lower back, and ribs.
uncommon
perioral tingling or paresthesia in fingers or toes
Indicative of hypocalcemic states.
Chvostek sign
Tapping on the face just anterior to the ear and seeing a twitching of muscles around the mouth. Seen in most hypocalcemic states. Demonstrates neuromuscular excitability.
Trousseau sign
Inflating blood pressure cuff above diastolic for about 3 minutes causes muscular flexion of the wrist, hyperextension of the fingers, and flexion of the thumb. Seen in most hypocalcemic states. Demonstrates neuromuscular excitability.
bowed legs or knock knees
Characteristic features of rickets in children. The weight of the body causes the abnormally mineralized skeleton to develop these classic rachitic deformities.
fractures
Feature of osteomalacia arising from SHPT. Fractures occur with even mild trauma or movement. Any bone may be affected, but long bone fractures are the most common.
Risk factors
strong
aging
Serum parathyroid hormone (PTH) levels increase as a function of age. Factors that may explain this include loss of renal capacity, calcium malabsorption, peripheral resistance to PTH calcemic effects, endemic vitamin D deficiency, and chronic metabolic acidosis.[21] Calcium intake in older patients is frequently insufficient precisely when their demand for this mineral is increased. This raises PTH levels, which has the undesirable consequence of skeletal resorption.[22] This is reversible with dietary supplementation.
The skin of older individuals also has a reduced capacity to synthesize vitamin D3 under the influence of ultraviolet light.[11][23]
chronic kidney disease
With decreased renal function, calcium and vitamin D are lost and result in a compensatory rise in parathyroid hormone (PTH). The presence of hypocalcemia and elevated PTH is classic for SHPT.[24] When phosphorus levels are also elevated, this points to chronic kidney disease (CKD) as the etiology.
Patients with CKD commonly develop renal osteodystrophy. If phosphorus levels are low, other anomalies such as vitamin D deficiency should be considered.[9]
vitamin D deficiency: inadequate sunlight exposure
Vitamin D deficiency is a global issue.[2] Inadequate direct sunlight exposure (or heavy/habitual sunscreen use) and inadequate vitamin D intake usually occur simultaneously to result in clinical vitamin D deficiency.
Casual sun exposure provides most people's vitamin D requirement.[2] Sunscreen with a SPF of 30, if used properly, can reduce the capacity of the skin to produce cholecalciferol by over 95%.[2] Consequently, those who always wear a sunscreen before going outside are at higher risk for vitamin D deficiency. Likewise, melanin in the skin of darkly pigmented individuals also acts to hinder vitamin D synthesis. A person with a skin type VI (dark brown, black) requires at least 5 to 10 times longer sun exposure than white people to produce adequate cholecalciferol in their skin.[2]
Particularly susceptible groups include older people (who may not be exposed to enough sunlight or are housebound, hospitalized, or institutionalized) and individuals who are confined to the home or who wear clothing that covers the entire body and face.[11] Other factors include season, geographic latitude, time of day during sun exposure, degree of skin pigmentation, cloud cover, and smog.[3][12][15] Ultraviolet-B radiation does not penetrate glass, so exposure to sunshine indoors through a window does not produce vitamin D.[2]
nutritional deficiency (especially absence of dairy products and fish)
Dairy products and fish are important sources of vitamin D and calcium. Diets deficient in these can contribute to poor intake of calcium and vitamin D deficiency.
vitamin D deficiency: malabsorption
Malabsorption is a common problem among older patients. One feature is reduced absorption of fats and, as vitamin D is a fat-soluble vitamin, this can contribute to hypovitaminosis D. This can be further aggravated by the fact that only small amounts of 25-hydroxyvitamin D are recirculated enterohepatically.[11][25] A history of celiac disease, Crohn disease, chronic pancreatitis, Whipple disease, or lactose intolerance can be a significant contributory factor to the development of vitamin D deficiency and poor calcium absorption.[15]
weak
vitamin D deficiency: hepatic dysfunction
vitamin D deficiency: genetic disorder
Type 1 hereditary vitamin D-dependent rickets is an autosomal recessive disorder characterized by absent or defective conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D in the kidneys.
Type 2 hereditary vitamin D-dependent rickets has several forms and is due to mutations in the 1,25-dihydroxyvitamin D receptor. This receptor affects the metabolism of gut, kidney, bone, and other cells. In this disorder, 1,25-dihydroxyvitamin D is abundant but ineffective because the receptor is not functional.[11][25]
X-linked familial hypophosphatemia is a genetic disease that causes high fibroblast growth factor-23 (FGF-23) levels, which in turn reduces vitamin D synthesis in the kidneys and increases the breakdown of vitamin D.[14]
vitamin D deficiency: obesity
Class III obesity (BMI 40 or above) has been associated with vitamin D deficiency and SHPT. In a case-control study, 90% of 41 prebariatric surgery patients had 25-hydroxyvitamin D levels <75 nanomol/L (versus 32% in controls), and 61% had 25-hydroxyvitamin D levels <50 nanomol/L (versus 12% in controls). Additionally, 49% of the prebariatric surgery patients had SHPT versus 2% of controls.[26]
Although vitamin D is fat soluble and is partially sequestered in the body fat to be used during the winter (when there is less sunlight exposure), in obese children and adults cholecalciferol is sequestered deep in the body fat, which reduces its bioavailability. Lower vitamin D levels likely reflect a volumetric dilution.[2][27] Consequently, obese individuals require larger than usual doses to correct vitamin D deficiency.[28]
medication use
Many anticonvulsants (phenytoin, phenobarbital) and glucocorticoids increase the need for vitamin D supplementation above basal requirements.[15]
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