Lead toxicity refers to poisoning due to ingestion or inhalation of products containing the element lead.
Cats may be exposed to lead from several different sources including:
Lead paint, paint chips and/or paint dust from homes that are being renovated or remodeled. Paints produced prior to 1977 contain high lead levels. This is a common source of lead to cats.
Lead weights used as sinkers on fishing poles.
Lead pellets and shot for use in guns.
Household items such as drapery weights, linoleum, rug padding, and foil from the tops of wine bottles.
Automotive parts such as batteries, wheel weights, leaded gasoline and discarded oil from cars using leaded gasoline.
Construction materials such as solder, putty and caulking.
Plumbing and roofing materials.
Kittens are more likely to ingest materials containing lead because of their normal chewing and play activities. Younger animals also seem to absorb larger amounts of lead from their gastrointestinal tract than do older animals. Cats from established urban environments are at higher risk for lead poisoning due to the presence of older buildings. Cats are at high risk due to their grooming behavior. When inhabiting a contaminated environment, cats may groom lead-based paint dust off their fur.
Lead toxicity can cause anemia (low red blood cell count), gastrointestinal symptoms (vomiting, diarrhea) and nervous system problems (seizures). Lead crosses the placenta from pregnant mother to babies and is also excreted in her milk. Thus, the developing fetus and nursing young can be affected.
What to Watch For
If you notice any of the following symptoms, call your veterinarian.
Loss of appetite
Increased thirst and urinations
Shortness of breath
Intolerance for exercise
Diagnostic tests are needed to recognize lead poisoning and confirm the diagnosis. Your veterinarian will take a complete medical history and perform a thorough physical examination. He may also recommend the following diagnostic tests:
A complete blood count (CBC or hemogram) to detect anemia, nucleated red blood cells, and other red blood cell abnormalities that often accompany lead poisoning ("basophilic stippling" of red blood cells).
Serum biochemistry tests to evaluate the general health of the dog, obtain baseline information about liver and kidney function before treatment, and assess the extent of systemic injury from lead poisoning.
Blood lead concentration gives the definitive diagnosis. Blood lead concentrations greater than 0.5 parts per million (abbreviated "ppm") are considered diagnostic of lead poisoning.
X-rays of the abdomen and chest are taken to check for lead objects in the intestinal tract and to evaluate the patient for evidence of an enlarged esophagus (which can be seen in lead poisoning) or pneumonia. Lead objects are dense and appear white or gray on the X-rays.
Lead concentrations in the feces can be used in place of blood lead concentrations to diagnose lead toxicity.
Gastric lavage (pumping the stomach) and enemas are performed to remove any remaining lead from the stomach and intestinal tract. Surgery can also be performed if necessary to remove lead objects from the intestinal tract.
Administration of chelating agents (drugs that bind lead in the bloodstream and facilitate its excretion from the body via the kidneys). These include calcium ethylene diamine tetra-acetic acid (Ca-EDTA), penicillamine, and succimer.
Fluids are administered intravenously to correct dehydration and facilitate urinary excretion of lead.
Anticonvulsant drugs such as diazepam (Valium®), phenobarbital or pentobarbital can be administered to control seizures.
Home Care and Prevention
There is no home care for lead poisoning. Seek veterinary care promptly if you suspect your pet has ingested lead-containing materials.
Administer as directed any medications prescribed by your veterinarian. Observe your pet's general condition. Note any symptoms that worsen and bring any changes to the attention of your veterinarian.
The most important part of preventing lead poisoning is to evaluate the dog's environment for potential sources of lead and remove them. If a source of lead has been identified and young children in the household have been exposed they should be evaluated by a pediatrician.
Keep cats away from areas in an older house (pre-1977) undergoing renovation or remodeling. Also keep cats away from discarded materials during re-roofing of homes. Prevent pet access to garages that may store lead-containing objects.
Lead toxicity may be acute, due to ingestion of a lead object, or it may be chronic due to repeated chewing of lead paint or grooming the dust of lead paint from the skin and fur. The most common route of exposure is ingestion but lead paint dust may also be inhaled.
Lead toxicity primarily affects the nervous system and gastrointestinal system. Common neurological symptoms include sudden onset of seizures, blindness, behavior changes, hysteria, chomping, muscle spasms and circling. Lead crosses the placenta and is excreted in milk, so it can affect unborn fetuses and nursing young.
Gastrointestinal signs include abdominal pain, loss of appetite, vomiting, and constipation or diarrhea. Some animals develop megaesophagus (enlargement of the esophagus and decreased ability to move food from the mouth to the stomach) resulting in regurgitation. Aspiration pneumonia may result from regurgitation. Lead toxicity may also suppress the immune system making cats more susceptible to infections.
With chronic exposure, lead is deposited in the tissues of internal organs (liver, kidneys) and in the bones. Lead that is deposited in the bones serves as a "reservoir" and can cause lead levels to remain high despite treatment in some patients. These cats often require long-term therapy.
Lead inhibits normal remodeling of the long bones of the body such as the femur, tibia, humerus and radius. As a result, specific areas in these bones look denser (whiter) on x-rays and these areas are referred to as "lead lines." Lead lines do not represent lead deposits in the bone.
The symptoms of lead toxicity are similar to the symptoms of the following diseases or toxicities:
Rabies virus can cause behavior changes and seizures. Cats with rabies often have a history of exposure to a wild animal or a history of bite wounds of unknown origin.
Epilepsy (seizures due to an abnormality in the brain) is typically seen in cats between the ages of 1-7 years. Epilepsy is idiopathic (of unknown cause), genetic, or secondary to trauma or another disease that caused structural changes in the brain. Epilepsy is diagnosed after exclusion of all other possible causes of seizures.
Thallium poisoning is rare but can cause gastrointestinal and neurological problems.
Strychnine poisoning can lead to seizures. Strychnine products are used to kill rodents but these products are rarely used in the United States.
Zinc poisoning can cause depression, loss of appetite, vomiting, diarrhea and anemia. The most common source of zinc is pennies minted after 1983, nuts, bolts and batteries. Zinc toxicity is differentiated from lead toxicity based on x-rays of the intestinal tract and measurement of blood zinc levels.
Chlorinated hydrocarbon poisoning (DDT, Chlordane, Dieldrin, Endrin, Aldrin, Chlordecone, and Endosulfan) is rare but can cause depression, vomiting, muscle tremors and seizures which look similar to symptoms caused by lead poisoning. Chlorinated hydrocarbons are used as insecticides.
A complete blood count (CBC) is usually done to look for changes in the red blood cells. Changes such as nucleated red blood cells (normal red blood cells do not have a nucleus) and basophilic stippling (blue granules) in the cytoplasm (area of the red blood cell surrounding the nucleus) are seen in 25 to 54 percent of animals with lead poisoning. Lead toxicity also causes anemia (decreased red blood cell count) and an elevated white blood cell count. Absence of these changes however, does not rule out lead poisoning.
A biochemistry profile is a blood test done to evaluate the function of internal organs. Elevation of liver enzymes is common in lead poisoning.
Measurement of blood lead levels is the diagnostic test of choice. A blood lead level of greater than 0.5 parts per million (ppm) is considered diagnostic. Blood levels of 0.35 to 0.5 ppm with the presence of symptoms are also considered diagnostic.
Thoracic and abdominal radiographs are done to look for lead objects in the digestive tract and to evaluate the esophagus for an increase in size (megaesophagus). Megaesophagus can lead to regurgitating and pneumonia, which may also be evident on x-rays. Negative x-ray findings do not rule out lead poisoning.
Fecal lead levels of greater than 35 ppm is suspect for lead toxicity.
X-rays of the legs may also be done to look for "lead lines" in the bone. In the area of a "lead line," the bone appears denser (whiter) than normal.
The foundation of treatment for lead poisoning involves administration of a chelating agent (drug that binds lead in the blood and allows the lead to be removed from the body). Only one chelating agent is used at a given time and the choice of chelating agent depends on availability. However, lead must be removed from the intestinal tract before beginning treatment with chelating agents, because these medications can increase the absorption of lead from the intestinal tract into the blood stream and worsening of the cat's symptoms.
Gastric lavage and enemas are used to remove lead objects from the stomach and intestinal tract. During gastric lavage, a large tube is passed through the mouth into the stomach. Water is pumped into the stomach and then drained, removing any stomach contents. This procedure requires sedation of the cat.
Surgery is indicated for removal of lead objects if they cannot be removed with gastric lavage and enemas.
Succimer is a chelator that is available in tablet form and is administered twice daily for 10 days. If the cat does not require hospitalization for his symptoms, the medication can be administered at home. Succimer can also be dissolved in water and administered rectally in unconscious patients.
Calcium EDTA is a chelator that is administered subcutaneously (under the skin) twice a day for five days during the time the patient is hospitalized. Calcium EDTA is not used in patients with pre-existing kidney disease and patients must receive fluids while they are on the drug. If blood lead levels remain high, Calcium EDTA treatment may need to be repeated beginning five days after the first treatment was finished. If the cat develops vomiting or diarrhea while on Calcium EDTA, your veterinarian may need to supplement zinc because Calcium EDTA chelates zinc as well as lead.
Penicillamine is a chelating agent that is given orally for long term use following Calcium EDTA therapy. Penicillamine is used primarily in patients with persistently elevated lead levels. This drug can be administered at home.
Placement of an intravenous catheter and administration of intravenous fluids is necessary for cats that are dehydrated and for cats that are receiving calcium EDTA.
Administration of anticonvulsants such as diazepam (Valium®), phenobarbital and pentobarbital may be necessary if the cat is having seizures. These drugs are usually only necessary during the period the cat is hospitalized and are rarely required long term.
Administration of thiamine (vitamin B complex) may help reduce some of the symptoms of lead poisoning although the mechanism is unclear. Thiamine is not a chelating agent.
Optimal treatment for your cat requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your cat does not improve rapidly.
Administer all prescribed medications as directed. Alert your veterinarian if you are experiencing problems treating your cat.
Prevent re-exposure to lead by removing the source responsible for the original intoxication.
Schedule an appointment with your veterinarian to recheck a blood lead level two weeks after therapy has been completed.