Cold Agglutinin Disease
Cold agglutinin disease has several variants. One rare variant affects young adults and usually occurs after infection with My-coplasma pneumoniae or infectious mononucleosis, although several cases have also been reported in association with chronic fal-ciparum malaria. A more common variant affects persons about 60 years of age and may present as idiopathic cold agglutinin disease, as a prodrome to a lymphoproliferative or an immuno-proliferative disorder, or in association with an already established lymphoproliferative disorder.153
Pathophysiology Serologically, cold agglutinin disease is characterized by the presence of high titers of IgM agglutinins (> 1:1,000 and usually > 1:10,000) in serum. These antibodies are maximally active at 4° C, are capable of activating the complement sequence, and are directed against the polysaccharide antigens. Presumably, IgM reacts with erythrocytes circulating in the cooled blood of the nose, ears, and shins, where it fixes complement and then dissociates from the RBCs when they reach warmer areas of the body.
In the postinfectious variety of this disorder, IgM cold agglu-tinin is oligoclonal and short-lived. Conversely, the IgM is monoclonal in chronic idiopathic cold agglutinin disease or in cases associated with Waldenstrom macroglobulinemia, chronic lym-phocytic leukemia, or other lymphomas. IgM predominantly contains X light chains in patients with chronic idiopathic cold agglutinin disease or Waldenstrom macroglobulinemia; in patients with lymphoma, however, the IgM mainly contains k light chains. Occasionally, the IgM cold agglutinin is detectable as an M protein spike on serum protein electrophoresis [see 12:XV Chronic Lymphoid Leukemias and Plasma Cell Disorders].
In the post-Mycoplasma variant, the mycoplasmas appear to bind to the RBC surface at the Ii antigen site. This receptor-ligand interaction results in the presentation of the I antigen in an im-munogenic form.154 Listeria monocytogenes contains the I anti-gen,153 further supporting the idea that some infectious agents stimulate the naturally occurring cold agglutinins, as well as cause the postinfectious cold agglutinin disease.
Diagnosis The clinical syndrome of cold agglutinin disease is quite variable. Patients occasionally show only low titers of cold agglutinins and have no other symptoms or have a history of recent pneumonia. In patients with warm-and-cold autoimmune hemolytic anemia, the associated hemolysis tends to be severe and chronic. The RBCs of these patients are coated with IgG and complement components, whereas their serum contains a relatively low titer of cold agglutinin that acts at 30° C and perhaps even at temperatures up to 37° C.
The diagnosis is suggested by hemolytic anemia with acral signs and symptoms. It may be difficult to draw blood, and the RBCs may visibly agglutinate in a cold syringe and on the blood smear. Automated blood cell counters may count the agglutinated RBCs as single cells and thus report absurdly high values for the MCV and MCHC. Usually, the laboratory detects a broadly active cold agglutinin. The direct Coombs test is positive with an-ticomplement reagents but infrequently positive with anti-IgG.
Findings that support the diagnosis of idiopathic cold agglu-tinin disease include a high IgM cold agglutinin titer with broad thermal reactivity134 and I specificity (reacting with erythrocytes from adults but not with cord erythrocytes), pure k light-chain composition, occasionally an absolute serum IgM elevation, and an M protein pattern on serum protein electrophoresis. Investigation should be directed at discovering a possible lymphoma or other underlying disorder in these patients. Conversely, post-Mycoplasma and post-infectious mononucleosis cold agglutinins are polyclonal. The post-infectious mononucleosis antibody is usually directed against i antigens (cord RBCs).
Treatment The post-Mycoplasma or the post-infectious mononucleosis variant is usually mild and self-limited and requires no specific treatment. Patients with the idiopathic variety who have acral symptoms must change their way of life, either by moving to a warmer climate or by keeping their ears, nose, hands, and feet covered during cold weather. In severely anemic patients, transfusions with packed RBCs may be required; in such patients, careful cross-matching and warming of the blood is necessary to minimize cold agglutination.
Splenectomy and corticosteroids are generally of no benefit in controlling hemolysis associated with cold agglutinin disease. Presumably, complement-coated cells are removed to a substantial degree by hepatic rather than splenic macrophages, and the cells that produce IgM are relatively insensitive to the effects of corticosteroids. Occasionally, however, high doses of cortico-steroids (e.g., 100 mg of prednisone a day) have resulted in a reduction in the hemolytic rate in patients with relatively low titers of cold agglutinins. In the relatively rare variant caused by IgG cold agglutinins, corticosteroids and splenectomy may be of benefit. Use of penicillamine or other reducing agents containing sulfhydryl groups produces no benefit. Good responses are occasionally obtained by the use of chlorambucil at a dosage of 4 to 6 mg/day. Exchange transfusion and plasmapheresis appear to be logical therapies for acute disease, but further clinical studies are needed to evaluate these techniques. Interferon alfa, at a dosage of 3 million U/m2 three times weekly, was reported to produce an impressive drop in cold agglutinin titer, with a decrease in serum IgM monoclonal protein and in acral symptoms over a 1-month period.134 Treatment with rituximab in the doses used to treat non-Hodgkin lymphoma has been beneficial.
Paroxysmal Cold Hemoglobinuria
Patients with the rare disorder of paroxysmal cold hemoglo-binuria have cold-induced signs and symptoms of intravascular hemolysis. The hemolysis is associated with the presence of an IgG serum antibody that is directed against the RBC’s P system. The IgG antibody is best demonstrated by the Donath-Land-steiner test; the serum is mixed either with the patient’s own blood cells or with blood cells from a normal person. The mixture is chilled to 4° C. If the IgG antibody associated with this disorder is present, hemolysis occurs after warming to 37° C. In the past, paroxysmal cold hemoglobinuria was usually seen as a complication of syphilis, but it has recently been observed in association with viral infections and non-Hodgkin lymphoma.
Hypersplenism
Hypersplenic disorders constitute a diverse group of clinical conditions sharing the common features of splenomegaly and he-molysis. Splenic enlargement and hemolysis occur in many disorders, including hepatic cirrhosis with congestive splenomegaly, Gaucher disease, lymphoma, connective tissue disorders, Felty syndrome, sarcoidosis, tuberculosis, and other infectious diseases.
Pathophysiology
The spleen’s unique structure accounts for several of the pathophysiologic features of hypersplenism. Splenic arterioles have a few direct branches leading to the sinusoids, but most of the terminal arterioles open into the splenic cords. Blood cells pass from the cords to the pulp through slits in the sinus walls; the slits have dimensions of about 1 by 3 Mm.158 Blood cells must squeeze through the longitudinal spaces, which are lined with reticular fibers, and between adventitial cells that are located outside the sinus. Macrophages and endothelial cells line the inside of the sinus. Repeated intimate contact occurs between blood cells and these macrophages.
Blood flow in the spleen is slow. The erythrocyte’s pH and oxygen tension level fall, glucose is consumed, and the cell’s metabolism is impaired. The hematocrit may increase, further elevating viscosity and resistance to flow. As a consequence, the blood cells are exposed to metabolic and mechanical stresses in the presence of macrophages and other leukocytes that can recognize cell membrane damage. As erythrocytes age, phagocytes remove defective surface areas, transforming the biconcave eryth-rocytes into rigid spherocytes or RBC fragments; these particles are later trapped and removed by the reticuloendothelial system. A big spleen has a greater than normal blood flow and exposes an unusually large proportion of blood cells to its culling activities. Thus, the problem in hypersplenism is essentially a quantitative one. A vicious circle may evolve in patients undergoing he-molysis, because hemolysis itself may cause splenomegaly.
Diagnosis
If the spleen is not palpable but the clinical situation is strongly suggestive of splenomegaly, ultrasonography or CT scanning may prove useful. Because blood cells other than erythrocytes are affected by a large spleen, the patient may be pancytopenic. Unless the underlying disease specifically involves the bone marrow, the marrow of patients with hypersplenism is generally hy-perplastic because of rapid regeneration of all affected cell lines. The peripheral blood smear is not diagnostic of hypersplenism.
Treatment
If hypersplenism is producing clinically significant complications and if therapy for the patient’s primary disease does not shrink the spleen, splenectomy may be necessary. Anemia, however, is not necessarily attributable to hypersplenism, irrespective of the size of the spleen. Hemodilution is another possible mechanism. Patients with massive splenomegaly who have very low hematocrit and hemoglobin values may have a normal RBC mass as assessed with the 51Cr technique. Massive splenomegaly often is associated with an increase in plasma volume that results in extraordinary hemodilution. Moreover, greatly enlarged spleens may contain a pool of erythrocytes that constitutes as much as 25% of the total RBC mass—in contrast to normal spleens, which have no such RBC pool. In patients with splenomegaly who have a true decrease in RBC mass, the underlying disease may act to reduce RBC production by suppressing erythropoietin production rather than by accelerating destruction. Therefore, it is prudent to determine RBC mass before making the diagnosis of hypersplenism.
Drugs and toxins as causes of hemolysis
Drugs Causing Oxidative Attack
Pathogenesis Dapsone, sulfasalazine, phenacetin, sodium perchlorate, nitroglycerin, phenazopyridine, primaquine,100 paraquat, and vitamin K analogues can insert themselves into the oxygen-binding cleft of hemoglobin. By this action, such agents can generate oxidizing free radicals, such as superoxide, hydrox-yl free radical, and peroxide. If the erythrocyte’s protective reducing mechanisms are overwhelmed [see Table 1], hemoglobin is oxidized to form Heinz bodies and methemoglobin. Sulfhemoglo-bin is also produced by oxidative attack. The molecule contains a sulfur atom in the porphyrin ring, which gives it a blue-green color. The source of the sulfur atom is not clear, but the presence of sulfur in the heme ring makes it a poor oxygen transporter.159 The RBC membrane may also suffer from oxidative attack. Damaged cells are removed in the reticuloendothelial system. Hemolysis is usually, but not invariably, extravascular, and Heinz bodies can be seen on a specially stained blood smear. The smear may also show the bite, hemiblister, or cross-bonded cells typical of oxida-tive attack on erythrocytes [see Figure 4]. Severe oxidative damage apparently causes hemoglobin to puddle at one side of the RBC, leaving a plasma membrane-enclosed hemighost in the remainder. Such hemighosts can be detected in the peripheral blood. Severe oxidative destruction is associated with increased methemo-globin levels and a decrease in RBC levels of GSH. The methemo-globin level is elevated. As little as 1.5 g/dl of methemoglobin or 0.5 g/dl of sulfhemoglobin can produce the physical finding of cyanosis. By contrast, 5 g/dl of reduced deoxyhemoglobin is required to produce comparable cyanosis.
Nitrites can oxidize hemoglobin to methemoglobin. Consequently, the recreational use of butyl and isobutyl nitrites as stimulants, psychedelics, and aphrodisiacs has led to clinical problems. When inhaled in usual amounts, these agents may produce a mild to modest increase in methemoglobin, raising its concentration from the normal level of 1% to 2% to as much as 20%. More extensive inhalation or ingestion of these agents has induced severe methemoglobinemia, characterized by methe-moglobin levels approaching 62%. Because methemoglobin does not carry oxygen, these high levels are accompanied by manifestations of tissue hypoxia such as headache, shortness of breath, lethargy, and stupor. Physical examination shows tachycardia, postural hypotension, and cyanosis; the venous blood is purple-brown.160 If untreated, it is likely to be fatal.
Diagnosis Diagnosis is based on a history of exposure to an oxidant drug or other toxin, together with characteristic peripheral blood smear findings and elevated methemoglobin measurements.
Treatment Treatment should restore normal methemoglo-bin levels. Management starts with the identification and withdrawal of the offending agent. Patients who have severe met-hemoglobinemia should be treated immediately with 1 to 2 mg/kg of methylene blue; the agent is infused intravenously in a 1 g/dl solution over a 5-minute period. In the presence of the RBC enzyme NADPH-methemoglobin reductase and adequate amounts of the electron donor NADPH [see Table 1], methylene blue is rapidly reduced to leukomethylene blue. This product in turn quickly reduces methemoglobin to hemoglobin. Cyanosis is thereby reversed, and the patient should turn pink immediately after the infusion. Several hours later, however, the patient may again become cyanotic, presumably because nitrates released from tissues reenter the peripheral blood at that time. Readminis-tration of methylene blue at a dosage of 1 mg/kg intravenously over a 5-minute period should restore normal hemoglobin levels.
Successful methylene blue therapy requires adequate supplies of NADPH. Patients who have abnormalities of the pentose phosphate pathway, such as G6PD deficiency, will not respond to this approach and should receive emergency exchange transfu-sions.160 Patients with very high levels of methemoglobin (at least 60%) or those whose smears contain many hemighosts should undergo exchange transfusion, perhaps with hemodialysis.100,160
Lead-Induced Hemolysis
Lead exposure results in hypertensive encephalopathy, neuropathy, and hemolytic anemia characterized by coarse ba-sophilic stippling in RBCs. The mechanism of lead-induced he-molysis is complex because the metal has several actions: it blocks heme synthesis, thus causing a buildup of RBC protoporphyrin; it produces a deficiency of pyrimidine 5′-nucleotidase161; and it attacks erythrocyte membrane phospholipids, producing potassium leak and interfering with Na+,K+-ATPase activity.
Diagnosis Screening for lead poisoning entails measuring the free erythrocyte protoporphyrin level (sometimes called the zinc protoporphyrin level), which is elevated because lead blocks the last step in heme synthesis. The diagnosis is confirmed by measuring blood and urine lead levels.
Treatment After the exposure to lead is stopped, use of a chelating agent such as edetate calcium disodium (CaNa2EDTA) may be considered. Treatment is started with 0.5 to 1 g of intravenous CaNa2EDTA, given over a period of 6 to 8 hours; the compound is given daily for 5 days.
After this initial course, 0.5 g of CaNa2EDTA is given as an intravenous bolus or intramuscular injection every 2 days for 2 weeks, during which time the urine lead levels are monitored. Alternatively, the initial 5-day course of CaNa2EDTA can be followed with oral penicillamine: 1 g a day is given for the first 7 days; the drug is withheld for the next 7 days; and during the final 7 days of the regimen, the dosage of 1 g a day is resumed and the urine lead level is measured at the end of the final day. Another study recommends giving 500 mg of penicillamine a day and continuing this dosage for 60 days after the patient has become asymptomatic.162
Venoms And Physical Agents as Causes of Hemolysis
Agents Causing Enzymatic Attack
Classic examples of attacking enzymes are the snake-venom or clostridial lecithinases (e.g., phospholipase C). Such enzymes attack the phospholipids of the membrane bilayer and produce RBC fragmentation, spherocytosis, and intravascu-lar and extravascular hemolysis. Disseminated intravascular coagulation and shock may occur. Prompt recognition and management of the primary disorder is critical, as is supportive therapy.
Venom from the brown spider, Loxosceles intermedia, releases sphingomyelinases and metalloproteinases that cleave the RBC membrane glycophorins. This in turn facilitates complement activation and lysis of affected RBCs.163
Physical Causes of Hemolysis
Freshwater drowning and accidental intravenous administration of sterile water can cause intravascular hemolysis by osmotic lysis. In such cases, RBCs swell and become spheroidal. Saltwater drowning can induce hemolysis by desiccating RBCs. Burns cause temperature-mediated denaturation of erythrocyte membrane polypeptides, resulting in hemolysis.
Infectious Diseases Causing Hemolysis
Malaria is the most important infectious cause of hemolysis. The resulting severe anemia causes the death of large numbers of pregnant women and 2- to 5-year-old children in sub-Saharan Africa. Plasmodium species, particularly P. falciparum, directly parasitize and destroy RBCs, but the anemia is a complex blend of impaired RBC production, hemolysis of parasitized and non-parasitized130 RBCs, and ineffective erythropoiesis.164 The diagnosis is made by pathognomonic findings on the blood smear; treatment is directed against the malarial parasite, with support of the circulation with RBC transfusions if required [see 7:XXXIV Protozoan Infections].
Other infectious causes of hemolysis Infection with M. pneumoniae and infectious mononucleosis can cause cold agglu-tinin hemolysis. Infection with H. influenzae type b can cause he-molysis. The major virulence factor of H. influenzae, polyribose ribosyl phosphate (PRRP), allows the organism to escape phagocytosis. When PRRP is released into the circulation, it binds to RBCs. The binding of anti-PRRP antibodies then leads to complement-dependent hemolysis.Patients infected with HIV or cytomegalovirus may have autoimmune hemolytic anemia (see above).
Clostridial sepsis can be devastating; the appearance of free plasma hemoglobin or hemoglobinuria should suggest this often fatal infection. Clostridium species are capable of sudden, explosive growth; they can release many enzymes, including phos-pholipases and proteases, that digest RBCs, producing intravas-cular hemolysis.
Some infections can cause splenomegaly and hypersplenic hemolysis. Meningococcemia or overwhelming gram-negative septicemia often produces disseminated intravascular coagulation and microangiopathic hemolysis.
Babesiosis is caused by a parasite that invades RBCs and that is transmitted from its rodent reservoir by the same ixodid tick that carries Lyme disease and human granulocytic ehrlichiosis. This disease is being more frequently diagnosed, particularly in New England. Immunocompromised persons, such as those with HIV, are more likely to have chronic and severe infections. The diagnosis has been made on peripheral blood smears, but polymerase chain reaction methods are more sensitive.
Hemolytic Associated with Liver disease
Anemia in patients with liver disease is often the result of a production defect rather than hemolysis, but cirrhotic patients may have congestive splenomegaly with hypersplenic hemoly-sis. Macrocytes (with or without B12 or folate deficiency) and target cells (caused by cholesterol elevation) are also common findings in such cases.
Spur cell anemia Severe liver disease, including alcoholic cirrhosis, may result in the formation of irregularly spiculated RBCs known as spur cells (acanthocytes).168 Spur cells have alterations in their membranes (a decreased ratio of phospholipids to cholesterol169) that shorten their survival, resulting in hemolytic anemia.
Other causes of Hemolysis
Copper Accumulation
In rare instances, Wilson disease, a metabolic disorder associated with excessive copper deposition, is first detected during a coincident episode of dramatic, acute hemolysis. The release of free copper into the serum and its subsequent entry into RBCs are thought to be the underlying hemolytic mechanism. In addition to affecting hexokinase levels, the intracellular copper appears to cause formation of oxygen radicals that react with and oxidize membrane components. Although no successful therapeutic intervention has been reported, penicillamine can be given at a dosage of 2 to 4 g once a day orally to reduce the free copper level. The administration of 1,000 to 2,000 IU of vitamin E (a-tocopherol) a day for several days may also be helpful if oxidative attack is an important factor.
Cardiopulmonary Bypass
Free plasma hemoglobin increases after cardiopulmonary bypass. The increase is thought to be caused by activation of the complement pathway, leading to deposition of the C5b-C9 attack complex on the RBC surface [see 6:IV Disorders of the Complement System]}70
