Cretinism in a Bear

• Iodine (deficiency)

Clinical signs

• A wild-born Ursus americanus - American black bear cub had small size (6.8 kg at about eight months of age), short stature, broadened face, prominent brow and short snout. In captivity it grew slowly, reaching 20.5 kg after a further 8 months, and was noted to be clumsy. (J414.43.w1)

Radiography

• Maxilla shorter than the mandible, cranial vault apparently larger than normal with thinning of bone, reduced opacity of the cranial vertebrae and slight mottling, small, dorsally displaced dens. On the elbows and carpi, persistent open physes (further open than in a normal cub of 11 months old) and incomplete ossification of the cuboidal bones of the carpus. (J414.43.w1)

C-T scan

• Skull: enlarged lateral ventricles, third ventricle, mesencephalic aquaduct and quadrigeminal cistern. Brain sulci appeared more distinct than usual. Brachygnathism. (J414.43.w1)
• Cervical vertebrae 1-3: Incomplete ossification of the cervical vertebrae. On the floor of the vertebral canal of C1, a soft tissue structure, "interpreted to be an incompletely ossified dens of the C2 vertebral body" and casing dorsal displacement of the spinal cord. (J414.43.w1)

Gross pathology

• Small carcass for age, in good condition. 
• Head: Facial dysmorphism, with widening of the calvarium, prominent brow ridge, maxillary brachygnathism, shortened snout and slight lateral bowing of the right mandible.
• Spine and appendicular skeleton: conspicuous physes to the vertebrae and long bones. C2 had an enlarged, cartilaginous dens. 
• CNS: moderate bilateral and symmetrical enlargement of the lateral ventricles, enlarged third ventricle.
• Thyroid: marked enlargement of both lobes, each 6.0 x 3.0 x 1.5 cm, joined by an isthmus of 10.0 x 1.0 x 4.0 cm, spanning the ventral trachea. The thyroid was pale pink, shading to white at the isthmus, which was finely macrocystic. 

(J414.43.w1)

Histopathology

• Thyroid: large irregular follicles, occasional papillary projections within the lumina of the follicles. Simple cuboidal epithelium lining the follicles, which were devoid of colloid. Rare mitotic figures in epithelial cells. Dense fibrovascular stroma supporting the follicles. In a normal bear, the thyroid had uniformly round follicles, lined by low cuboidal epithelium and filled with colloid (homogenous eosinophilic matrix). (J414.43.w1)
• Long bones: physes showed morphologically normal endochondral ossification. (J414.43.w1)
• Dens: central area of trabecular bone and a large surrounding mantle of hyaline cartilage. (J414.43.w1)

Serology

• Serum T3 0.66 ng/mL, serum T4 < 1.0 µg/dL. (J414.43.w1)

• History & Documentation
• Physical Examination of Mammals
• Necropsy of Mammals
• Environmental Assessment
• Treatment and Care
• Environmental and Population Management
• Preventative Medicine for Mammals
• Chapter 2 - B36 Field Manual of Wildlife Diseases - Specimen Collection and Preservation
• Chapter 3 - B36 Field Manual of Wildlife Diseases - Specimen shipment
• Appendix A - B36 Field Manual of Wildlife Diseases - Sample specimen history form

• Bears (Ursidae - Bears (Family))
• Ursus americanus - American black bear

List does not contain all other species groups affected by this disease. [N.B. Miscellaneous / Traumatic Diseases tend to be under-reported and the majority are likely to affect all bird and mammal species, given exposure to the related disease agents/factors.]