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CASE HISTORY • Part 1
A 47-year-old man presents with palpitations, shortness of breath, and marked asthenia. Past history and review of systems (ROS) are positive for more than 10 years of arthralgia/arthritis of both small and large joints, progressive loss of libido, and recent weight loss. Vital signs: BP - 135/80 mm Hg, P - 96 bpm, R - 16 bpm. Examination reveals a tanned, anxious white male; irregular pulse without cardiomegaly or murmurs; slight hepatomegaly; no obvious joint deformity; and testicular atrophy. Initial studies:
CBC: Hematocrit/hemoglobin - 42%/14 g/dL
MCV - 90 fL MCH - 32 pg MCHC - 33 g/dL
White blood cell count - 7,200 /μL with a normal differential
Platelet count - 190,000/μL
SMEAR MORPHOLOGY Normocytic and normochromic with normal white cell morphology.
Reticulocyte count/index - 1%/1.0
Blood chemistries: Fasting glucose - 150 mg/dL
Slightly elevated AST and ALT
Serum iron - 270 μg/dL TIBC - 300 μg/dL
Serum ferritin - 2,360 μg/L
ECG - Atrial fibrillation, left bundle hemiblock and strain pattern
Questions Given the patient's history and laboratory findings, what diagnosis comes to mind?
What additional laboratory tests are indicated?
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Excessive iron loading of tissues (hemochromatosis) can result from a primary genetic defect or as a complication of liver disease and certain anemias. Genetic predisposition to excess iron absorption (hereditary hemochromatosis) is especially prevalent in European populations; approximately 1 of every 8 individuals of Celtic or Northern European stock is heterozygous for the most common HFE gene defect, while 1 of 200 is homozygous. In addition, a number of other less common genetic defects involving steps in the regulation of iron absorption and storage have now been identified by genetic analysis in non-European populations. Patients with liver disease, pancreatic dysfunction, and certain erythropoietic disorders can also demonstrate significant iron loading, leading to tissue damage.
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The major pathways of iron metabolism are described extensively in Chapter 5. Most of the body's iron is incorporated in hemoglobin, myoglobin, and iron-containing enzymes (see Table 5-1). The amount of iron bound to the transport protein, transferrin, is only 3 mg. Reticuloendothelial iron stores vary according to the patient's sex and diet. Adult males have up to 1,000 mg of reticuloendothelial iron stores, whereas children and menstruating females rarely have more than 200 mg.
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Iron Storage, Transport, and Absorption
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Iron is stored intracellularly as ferritin and hemosiderin. Ferritin synthesis is regulated according to iron availability by a system of cytoplasmic iron binding proteins (IRP-1 and -2) and a noncoding, mRNA iron regulatory element (IRE). With iron deficiency, binding of IRP to the mRNA IRE inhibits the translation of isoferritins. When abundant, iron blocks binding and promotes an increased synthesis of ferritin. In the absence of organ damage, primarily liver damage, serum ferritin is in equilibrium with tissue stores, and therefore can be used as ...