Specimen: One guinea pig carcass in fair post mortem condition.
Necropsy: General -- Guinea pig was in good nutritional condition with body condition score of 3.5 out of 5. Alimentary System -- Small intestinal loops were multifocally congested and hemorrhagic. Pancreas was pale gray with small white foci. Small intestinal loops were partially fluid filled and partially filled with pasty red material (hemorrhage). Liver was slightly discolored. Stomach was distended, filled with yellow brown fluid. No significant lesions were noted in other organ systems.
Histopathology: Liver -- Hepatocytes are multifocally, slightly vacuolated with mostly clear, membrane bound vacuoles (lipid) and less often with indistinct, fuzzy vacuoles (glycogen). Lung -- Some pulmonary arteries have marked thickening of tunica media. Multifocally, there is accumulation/infiltration of adipocytes surrounding pulmonary arteries and bronchi. Heart -- Sparse numbers of lymphocytes, plasma cells and few heterophils are sprinkled within epicardial adipose tissue. In addition, small aggregate of neutrophils is present in the myocardium adjacent to ventricular lumen. Kidney -- In both renal sections there is marked accumulation of eosinophilic homogenous material deposited mostly in renal medulla. Multifocal to coalescing tufts of this material surround and separate slightly degenerate tubules that occasionally are mineralized, lined by flattened epithelial cells. Similar material occasionally thickens basement membranes of cortical tubules and Bowman's capsules of glomeruli. Only rarely such material completely effaces whole glomerulus. Uterus -- Lamina propria is nearly diffusely infiltrated with moderate numbers of lymphocytes and plasma cells. Pancreas -- Pancreas is markedly atrophied with small remnants of pancreatic lobules separated by abundant amount of adipose tissue. Islets of Langerhans are poorly preserved, commonly surrounded by multifocal to coalescing deposits of eosinophilic slightly fibrillar material indicative of amyloid. Similar material is occasionally present in the walls of the blood vessels. Bone marrow -- Marrow is on average 30% cellular with all cell populations represented. Myeloid to erythroid ratio is 2:1 with relative predominance of myeloid series. No significant lesions were seen in sections of brain, thyroid gland, adrenal gland, colon, ovary, and oviduct. Small intestinal and gastric sections were too autolytic for interpretation.
Bacteriology: Aerobic bacterial cultures of small intestine, liver and lung resulted in no significant growth. Aerobic cultures of small intestine were negative for Clostridium perfringens. Colonic and pooled tissue cultures for salmonella in selected media were negative.
Toxicology: Hepatic ICP analysis for trace mineral and heavy metal levels has been completed. Results are enclosed. Although we don't have normal reference range levels for guinea pigs due to few submissions, according to mineral level reference book by Puls, mineral levels detected in this guinea pig were within normal limits.
Summary: (Preliminary)
1. Kidney -- Renal medullary fibrosis or amyloidosis, extensive, severe with tubular degeneration; testing in progress.
2. Pancreas -- Exocrine pancreatic atrophy with amyloidosis in islets of Langerhans.
3. Heart -- Epicarditis and myocarditis, lymphocytic and suppurative, minimal, multifocal.
Comments: Bone marrow was evaluated and appeared to be normal with slight predominance with myeloid series. Heterophils are the counterpart of neutrophils in guinea pigs and may be confused with eosinophils. Renal lesions may be compatible with renal medullary fibrosis or amyloidosis. Special stains to distinguish these two extracellular matrices are in progress. Renal lesions were severe and may be compatible with renal insufficiency. Exocrine and pancreatic atrophy is commonly encountered in older guinea pigs and may not necessarily result in exocrine pancreas insufficiency.
Addendum: 11/14/02 Special stains: Material deposited in the renal medulla and to lesser extent in the basement membranes of tubules and glomerular Bowman's capsules was confirmed as amyloid. Testing of pancreas and brain (per owner's request) is in progress.
Summary (final):
1. Kidney -- Renal medullary amyloidosis, extensive, severe with tubular degeneration.
11/19/02 Special stains: Presence of amyloid in pancreatic islet cells was confirmed by Congo red stain. Amyloid was not detected in brain sections.
01/02/03 Histopathology: No significant changes were seen in the section of spleen. Comment: Amyloid is most likely reactive (secondary; amyloid SAA) since no plasma cell tumor was seen that would account for production of immunoglobulin light chains (primary amyloidosis, amyloid protein AL). Another form of amyloidosis in animals is familial form seen in the shar-pei dog and the Abyssinian cat. No such information is available for guinea pigs.
Ilze Matise, DVM, PHD
jlk cc: Joanne C. Mueller 731 123rd Ave NW Coon Rapids, MN 55448 Tel 763-755-6114; Cell 612-747-3625
