65

65 CASE 65


A 58-year-old woman is referred to an internist due to high calcium levels found during treatment for a fracture of her femur.


The patient’s femur was fractured at the midshaft by a compression. The injury should not have been severe enough to break the bone. During treatment, the patient was noted to have high calcium levels and was referred for further study.



PHYSICAL EXAMINATION



VS: T 37°C, P 80/min, R 15/min, BP 116/76 mm Hg, BMI 26

PE: The patient appears healthy and exercised regularly before the injury. The left femur is immobilized, and the injury appears to be healing well.


LABORATORY STUDIES



Plasma analysis:
• Serum calcium: 14.2 mg/dL (normal: 8.4-10.2 mg/dL)

• Serum phosphorus (inorganic): 2.1 mg/dL (normal: 3.0-4.5 mg/dL)

• PTH levels: 2200 pg/mL (normal: 230-630 pg/mL)


DIAGNOSIS


Hyperparathyroidism



PATHOPHYSIOLOGY OF KEY SYMPTOMS


The patient’s major symptoms are tied to bone integrity and calcium balance. Bone weakness can be localized, for example, owing to poor circulation or a growing tumor. Alternatively, the bone weakness can be generalized phenomena affecting all the bones in the body. Compromised bone integrity can be due to the loss of the organic bone matrix or the loss of calcium hydroxyapatite crystals.


Within the body, calcium balance is maintained by regulating dietary intake and absorption against renal excretion. Ninety-nine percent of body calcium is stored in bone complexed to phosphate as hydroxyapatite crystals. The remaining 1% is distributed within the cells (particularly the endoplasmic sarcoplasmic reticulum) and in the extracellular fluid. Normal plasma calcium concentration is 10 mg/dL, 50% of which circulates as ionized (free) calcium, 40% complexed to plasma proteins, and 10% complexed to phosphate, citrate, and other nonprotein anions. Ionized calcium levels represent the balance between dietary absorption, exchange with storage pools, and renal excretion (Fig. 65-1).


image

FIGURE 65–1 Parathyroid hormone increases free plasma Ca++. Free plasma Ca++ represents the balance between dietary Ca++ uptake, exchange with the bone Ca++ storage pool, binding to PO4, and renal Ca++ loss. Parathyroid hormone increases dietary Ca++ uptake by increasing vitamin D synthesis, increases osteoclast activity to release Ca++ stored in the bone, increases renal PO4 excretion, and decreases renal Ca++ excretion. All these actions increase free plasma Ca++ levels.

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Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on 65

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