Conference 21 - 2016 Case: 2 20170329

Signalment:

Five-month-old Hereford-crossbred steer (Bos taurus).Calves fed potatoes, 1 death in the herd. Calf showed neurological signs, focal seizures, blindness, head pressing. No response to thiamine or florfenicol.

Gross Description:

The brain gyri were swollen and flattened. The rumen pH was 8, and the rumen contained two, small balls of plastic bags. The jejunum had several Monezia expansa cestodes. The costochondral junctions had a 7mm-thick, dense line of presumed cartilage core retention. Radiographs of thin sections have a dense white line.

Histopathologic Description:

A section of decalcified rib costochondral junction is examined. The zone of proliferating chondrocytes is longer than expected and proliferating chondrocytes can be seen in trabeculae far into the rib in retained, calcified cartilage. The invasion into chondrocytes is uneven, and while osteoblasts pile up in the hollow profiles of early-calcified chondrocytes, osteoclasts do not extend into these chondrocytes. The chambers of the initially invaded chondrocytes have erythrocytes, and a punctate, <2um basophilic dusting often fills these early chambers. The provisional calcified cartilage is retained far into the rib marrow space with only thin, apposed osteoid/bone. The provisional bone is thick and retained. Some osteoclasts are free in the marrow as opposed to being apposed to surfaces. Osteoclasts show more ani-socytosis with both size and shape variation and variable numbers of nuclei (osteoclastic dysplasia). Many dysplastic osteocytes have large, round and multiple inclusions. Bone marrow is otherwise hypocellular with serous degeneration of fat, and normal marrow constituents of the rib appear more distal from the costochondral junction than in a normal physis.

Morphologic Diagnosis:

Rib, physis: chondrodystrophy with osteo-sclerosis, retained calcified cartilage; osteoclast dysplasia/hyperplasia.

Lab Results:

Blood lead concentration: 0.7 ppm (normal <0.3 ppm) Kidney lead concentration: 6.2ppm (Normal: 0.1-1.0 ppm) Hematocrit: 31%.

Condition:

Lead toxicosis, physeal dysplasia

Contributor Comment:

Costochondral line examination is part of a routine diagnostic necropsy examination. It demonstrates nutritional imbalances in any production mammal, or as in this case, mineralized cartilage retention usually due to osteoclast problems such as with BVDv persistently infected calves, canine distemper (Thompson 2007), and in our case, lead poisoning. Unfortunately, many people do not do it routinely.

The bone lesions of lead poisoning were well described in the early 1930s by several authors studying poisoned children, and those descriptions remain valid. (Reviewed by Park 1933). The lead line in children will form once blood lead is 70-80 ug/dl. One month after treatment with chelating agents, the line separates from the zone of proliferating chondrocytes, and it will disappear in 4 years (Sachs 1981). Later descriptions added electron microscopic findings indicating that osteoclasts often lost their ruffled border and were less intimate with the surfaces (Eisenstein 1975). Nuclear and cytoplasmic inclusions were seen with EM. The cytoplasmic inclusions increased in size in osteoclasts more distant from the physis (inclusions fused?). Ultimately, morphologists concluded there is an inability for chondroclasts/osteoclasts to remove metaphyseal calcified cartilage cores presumably because they cannot degrade (or excrete) it. They are thus constipated.(Eisenstein 1975) Interestingly, lead binds to osteocalcin to make a more compact molecule, and lead can cause a 40% increase of hydroxyapatite mineral over that bound with calcium (Dowd 2008). Might such modifications lead to indigestion- to continue the ANALogy (JFE)? The increase in osteoclasts is a compensatory hyperplasia. Lead poisoning-induced, osteoclast intra-nuclear inclusions are visible with electron microscopy (Hsu 1973). These inclusions of lead and protein aggregates are best-known in proximal renal tubules (where they make up 90% of the lead in kidneys), but are also in osteoclasts and less frequently in hepatocytes and glia (Goyer 1970, Moore 1974). Experimental and spontaneous studies demonstrate they may appear and regress in intoxicated individuals (Hzu 1973, Hamir 1983, Goyer 1970). EM shows them more frequently, and they are seen occasionally in light microscopy using Ziehl-Neelsen acid-fast stain. We could not see them reliably with acid-fast or PAS staining. In experimental lead poisoning of dogs (Zook 1972), metaphyseal sclerosis with retention of cartilage trabeculae having more mineralized cartilage with increased numbers of large osteoclasts distal from the physis were seen.

Obviously, the lines are seen in young animals forming bones. Lead intoxication is more common in calves and thus are seen during calving season. Cattle usually have exposure to old lead base paints, discarded lead batteries, solder, linoleum, mining, smelting, and crankcase oil (ingested or used on skin as an insect repellant!) in pens or pastures (Blakley 1984, Burren 2010). Sometimes, recycling materials are incriminated (Payne 2008). Cases where pastures are previous shooting ranges have produced lead intoxications (Payne 2013). The decreased use of leaded gasolines has reduced risk of lead poisoning (Burren 2010). Blood, liver and kidney are favored samples to measure lead. When examining blood, many animals having measurable blood lead will not show signs (diarrhea, seizures, bruxism, blindness, hemorrhages). The half-life of lead in exposed cattle is 135 days, std deviation 125 days (Bischoff 2012, Voigt 2010). Our calf was ill and had laminar cortical necrosis. Unfortunately, a specific lead source in this case was not found, and a farm visit was not allowed. The potatoes mentioned in the history were never provided and are considered a red herring.

JPC Diagnosis:

one bone: Physeal dysplasia, with retention of cartilage cores, and focal necrosis, Hereford-crossbred steer, Bos taurus.

Conference Comment:

We thank the contributor for his thorough and often satirical review of the skeletal lesions associated with lead toxicity in a young growing animal. The excellent quality gross image and radiographs provided by the contributor nicely demonstrate the thick band of sclerosis present in the metaphysis, known as the lead line mentioned above. Normally, growth of the bone at the metaphysis is the result of an orderly balance between osteoblastic deposition of bone and osteoclastic bone resorption at the zone of provisional calcification in the physeal zone of hypertrophy and primary spongiosa.^4,11 The majority of lead is stored within osseous tissues of the skeleton, and lead ions will preferentially deposit within the metaphysis and directly inhibit osteoclastic activity at this location.¹⁶ As a result of this impairment of osteoclastic resorption of bone within the primary spongiosa, there is disruption of endochondral ossification and the formation of a growth retardation lattice.^4,11,16 This lattice is composed of elongated and vertically oriented trabecular bone with persistent cores of mineralized cartilage within the metaphysis. The sclerotic metaphysis is not radiopaque due to the lead itself; rather it is a result of calcium deposition and retention of mineralized cartilage trabeculae within the metaphysis.^4,11 As mentioned by the contributor, other diseases that cause growth retardation lattices include canine distemper virus (canine morbillivirus) and bovine pestivirus. Both viruses infect osteoclasts resulting in reduced bone resorption.^4,11

This case generated spirited discussion among conference participants regarding whether the histologic lesions described in this case are consistent with lead intoxication. Conference participants described a diffusely thickened growth plate with multifocal tongues of cartilage cores extending into the metaphysis with a light blue to pink matrix and surrounded by a necrotic coagulum. Participants also noted few large vacuolated osteoclasts containing up to thirty nuclei within Howships lacuna but were not able to identify intranuclear or intracytoplasmic inclusions noted by the contributor.

Prior to the conference, the moderator, Dr. Linden Craig, examined the long bones of several age-matched control calves without lead intoxication. The consensus opinion of the conference moderator and participants is that there is no significant difference between the amount of mineralized cartilage trabeculae in the calf from this case and an aged matched control animal. This represents a disconnect between the sclerotic metaphysis seen both grossly and radiographically in this case, and the histologic appearance which lacks the significant retention of mineralized cartilage trabeculae within the metaphysis when compared to the rib of age-matched control. Some participants posited that this may be an artifact of decalcification processing of this section. Without the aid of the gross, radiographic, and historical data, diagnosis of lead intoxication in this case is extremely difficult.

References:

1. Bischoff K, Thompson B, Erb HN, Higgins WP, Ebel JG, Hillebrandt JR. Declines in blood lead concentrations in clinically affected and unaffected cattle accidentally exposed to lead. J Vet Dign Invest. 2012; 24:182-7.

2. Blakley BR. A retrospective study of lead poisoning in cattle. Vet Hum Toxicol. 1984; 26: 505-7.

3. Burren BG, Reichmann KG, McKenzie RA. Reduced risk of acute poisoning in Australian cattle from used motor oils after introduction of lead-free petrol. J Aust Vet Asso. 2010; 88: 240-241.

4. Craig LE, Dittmer KE, ThompsonKG. Bones and joints. In: Maxie MG, ed. Jubb, Kennedy and Palmers Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Elsevier Ltd; 2016:16-87.

5. Dowd TL, Li L, Gundberg CM. The 1H NMR structure of bovine PB2-osteocalcin and implications for lead toxicity. Biochim Biophys Acta. 2008; 1784:1534-45.

6. Eisenstein R, Kawanoue S. The lead line in bon-A lesion apparently due to chondroclastic indigestion. Am J Pathol. 1975; 80: 309-16.

7. Goyer RA, May P, Cates M, Krigman MR. Lead and protein content of isolated intranuclear inclusion bodies from kidneys of lead-poisoned rats. Lab Invest. 1970; 22:245-251.

8. Hamir AN, Sullvan ND, Handson PD. Acid fast inclusions in tissues of dogs dosed with lead. J Comp Pathol. 1983; 93:307-17.

9. Hsu FS, Krook L, Shively JN, Duncan JR. Lead inclusion bodies in osteoclasts. Science. 1973; 181:447-8.

10. Moore JF, Goyer RA. Lead-induced inclusion bodies. Composition and probable role in lead metabolism. Environ Health Perspec. 1974; 7:121-7.

11. Olson EJ, Carlson CS. Bones, joints, tendons, and ligaments. McGavin MD,ed. Pathologic basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier Mosby; 2017:964-965.

12. Park EA, Jackson D, Goodwin TC, Kajdi L. X-ray shadows in growing bones produced by lead; Their characteristics, cause, anatomical counterpart in the bone and differentiation. J Pediatr. 1933; 3: 265-300.

13. Payne JH, Holmes JP, Hogg RA, van der Burgt GM, Jewell NJ, Welchman G de B. Lead intoxication from clay pigeon shooting. Vet Rec. 2013; 173:552-4.

14. Payne J, Otter A, Cranwell M, Jones J, Wessells M, Whitaker K. Lead poisoning associated with recycled wood products. Vet Rec. 162: 191-2.

15. Sachs HK. The evolution of the radiographic lead line. Radiol. 1981; 139: 81-85.

16. Thompson K: Bones and joints. In: Maxie MG ed. Jubb Kennedy and Palmers Pathology of Domestic Animals, 5^th edition. Saunders Elsevier New York; 2007:53-54.

17. Voigt K, Benavides J, Rafferty A Howie F, Buxton D. Lead poisoning in calves with eosinophilic meningitis. Vet Rec. 2010; 167:791-2.

18. Zook BC. The pathologic anatomy of lead poisoning in dogs. Vet Pathol. 1972; 9, 310-327.