Page 1054 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

H aemolymphatic system 1029

VetBooks.ir Prognosis 9.32
Successful treatment of EPH depends on aggres-
sive early therapy and absence of secondary organ
damage and sepsis. A mortality rate of 30% has been
reported. With significant skin sloughing, the prog-
nosis is poor. The recovery period can be quite long,
depending on the occurrence of complications, and
the prognosis becomes poor if the initial response to
therapy is inadequate.

LEAD TOXICITY

Definition/overview
Lead poisoning can occur when animals graze pas-
tures contaminated by nearby lead smelters or other Fig. 9.32 Lead toxicity. Basophilic stippling in RBCs
sources of lead including old batteries, discarded (arrows) (Wright’s stain).
motor oil, machinery grease and roofing materials.
Although haematological abnormalities occur, neu- kidney, bone). In chronically poisoned animals,
rological signs tend to predominate. however, blood lead concentrations may be within
the reference interval because of deposition in bone.
Aetiology/pathophysiology In these instances, measurement of free erythro-
Absorbed lead inhibits certain enzymatic reactions cyte porphyrins or ALA concentrations may be
and interferes with zinc-containing metalloproteins. useful. Determination of lead concentration in soil,
Enzymes involved in heme synthesis are especially pastures or other contaminated materials to which
sensitive to the effects of lead. Interference with animals had access could also facilitate diagnosis.
aminolevulinic acid (ALA) dehydratase, ferrochela- Although anaemia is usually not present, abnormal
tase and 5’-nucleotidase results in an accumulation features on the blood smear may include poikilocy-
of porphyrins, decreased erythrocyte lifespan and tosis, anisocytosis, basophilic stippling and meta-
basophilic stippling of RBCs. rubricytosis (Fig. 9.32).

Clinical presentation Management
Neurological signs, including ataxia, dysphagia, laryn- The source of contamination should be removed
geal and facial paralysis, proprioceptive deficits and to eliminate further poisoning. Specific treatment
masticatory problems, predominate. Dysphagia and requires chelation with calcium disodium EDTA
pharyngeal paralysis may result in aspiration pneumo- (75 mg/kg slow i/v in 5% dextrose in water, or saline
nia. Hyperaesthesia, muscle fasciculations, blindness divided into 2–3 daily doses for 4–5 days, stop treat-
and head pressing may occur, but are more common in ment for 2 days, then repeat for 4–5 days). Thiamine
other species. Weight loss can be a prominent feature (0.5–5.0 mg/kg i/m q24 h) may also have a beneficial
and the animal may terminally have seizures. effect. Supportive care, including anticonvulsants,
intravenous fluids and nutritional support, may be
Differential diagnosis required. Broad-spectrum antimicrobial therapy
Other neurological diseases, such as botulism, teta- is indicated if aspiration pneumonia is present or
nus and other neurotoxins, need to be ruled out. suspected.

Diagnosis Prognosis
Definitive diagnosis is made by identifying abnor- Affected horses may recover with appropriate
mally high levels of lead in blood or tissues (liver, therapy.