What do muscle wasting and weight loss tell you about a case?

Signalment

Canine, Labrador Retriever cross, 8 years/4-month-old, male castrated, 52.4 lbs.

Clinical history

The dog presents for vestibular signs (responds to steroids and meclizine therapy and relapses when off of meclizine), generalized muscle wasting and weight loss.

Physical examination

The findings include rectal temperature 102.3° F, heart rate 60-70/min (restored to a normal heart rate with glycopyrrolate administration), respiratory rate 35/min, pink mucous membranes, normal capillary refill time, body condition score 2/5, and normal heart and lung sounds. The cranial nerves examination is normal. There is subtle cloudiness of right tympanum, apparently normal left tympanum and generalized muscle wasting. Last therapy has included enrofloxacin and meclizine.

Laboratory results

A complete blood count, serum chemistry profile, and urinalysis were performed and are outlined in Table 1.

Table 1: Results of laboratory tests

Thyroid panel

The serum T4 value (RIA) is 1.49 (normal range 1.0-4.0 µg/dl); the serum free T4 value (RIA) is 0.86 (normal range 0.65-3.00 ng/dl). The dog has not been receiving any thyroid supplementation.

Skull radiographic examination

Lateral and open mouth skull radiographs were obtained.

My comments

The right tympanic bulla is distorted and difference in general appearance from the left tympanic bulla. There is cloudiness in the right tympanic bulla.

Photo 1

Case management

In this case, most likely vestibular signs as caused by right chronic otitis media/interna is the clinical diagnosis. The generalized muscle wasting and weight loss is most likely related to some type of nerve or muscle disease. I doubt that the otitis media/interna caused the generalized muscle wasting but could cause some weight loss. The potential muscle or nerve disease could be related to an immune-mediated disease; hence, a polymyositis or polyneuropathy. I really do not believe a brain tumor is involved. It could be possible that this dog could benefit from some short-term steroid administration.

Wrong interpretation

Because of the dog's worsening vestibular signs, the dog underwent MR imaging of the skull. T1-weighted and T2-weighted transverse images were first obtained. Intravenous contrast medium was administered and T1W transverse, sagittal and dorsal images were acquired. The findings of the MR imaging were as follows.

Photo 2

There is a 2-cm discretely bordered mass within the left half of the cerebellum with extension toward the brain stem and specifically includes the left seventh and eighth cranial nerves. This mass is mostly isotense to the normal brain tissue on T1-weighted images, but diffusely hyperintense on T2-weighted images.

The mass enhances with the contrast medium. The mass contains multiple, non-enhancing low T1-weighted and high T2-weighted signal foci consistent with cysts. The fourth ventricle is compressed and deviated to the right by the mass. The bullae and ear canals appear within normal limits.

MR diagnosis

Choroid plexus tumor arising from the cerebellopontine angle or fourth ventricle. Obstruction of the fourth ventricle is highly likely as this mass progresses and will lead to obstructive hydrocephalus.

Review of brain tumors

Brain tumors may be primary (arising from tissue inherent to the brain and its coverings) or secondary (reaching the brain by local extension or hematogenous metastasis).

The most common primary tumors of dogs are neuroepithelial (gliomas), meningeal (meningiomas) and lymphoid (reticulosis, lymphosarcoma) in origin. Glial cell neoplasms and pituitary gland tumors occur most commonly in brachycephalic breeds, while meningiomas are recognized most often in dolichocephalic breeds.

The brain is the most common site for metastasis of systemic neoplasms. Secondary tumors that are commonly associated with metastatic brain disease include nasal adenocarcinoma with its direct extension and distant metastasis from melanoma, hemangiosarcoma, mammary gland adenocarcinoma, pancreatic adenocarcinoma, undifferentiated carcinomas and adenocarcinoma of multiple origins.

Clinical signs

Regardless of whether the brain tumor is primary or metastatic, clinical signs are usually slowly progressive over several weeks to months or may be rapid in onset and have a short clinical course. Most dogs with brain tumors will have long histories of vague signs that may be overlooked until signs of brain dysfunction are well advanced.

The clinical signs of brain neoplasms include anorexia, seizures, altered behavior, circling, head pressing, compulsive walking, altered consciousness and locomotor disturbances.

Cerebral tumors will typically cause behavior changes, seizures, visual deficits and circling. Brain stem tumors will typically cause depression, head tilt, cranial nerve deficits, weakness and ataxia. Cerebellar tumors will typically cause ataxia, head tilt, circling and tremor.

Choroid plexus tumors may also include signs of vomiting and bradycardia. Acute onset of blindness and dilated non-responsive pupils may be the only clinical signs of an intracranial tumor and are usually located in the chiasmal region.

Survey skull radiographs, cerebrospinal fluid analysis and/or special imaging techniques such as computerized tomography or magnetic resonance imaging are commonly incorporated in the clinical evaluation of a suspect dog for neoplasia of the central nervous system.

Survey skull radiographs are of limited value in the diagnosis of a primary brain tumor; however, they may be helpful in the detection of neoplasms of the skull or nasal cavity that have affected the brain by local extension. Radiographs of the skull may occasionally reveal erosion or hyperostosis of the calvarium in association with a primary brain tumor (e.g., meningioma) or document areas of mineralization within a neoplasm.

Fluid analysis

Cerebrospinal fluid analysis is often helpful in evaluating dogs suspected of having an intracranial tumor, especially if the tumor communicates with the ventricles or subarachnoid space.

Although, cerebrospinal fluid changes are often nonspecific, when combined with the history and neurologic examination, such changes may provide an accurate diagnosis. Cerebrospinal fluid analysis may reveal a definitive diagnosis if neoplastic cells are visualized, but this is unusual unless its lymphosarcoma. Unless neoplastic cells are present, the cerebrospinal fluid analysis will provide only indirect evidence that a tumor exists. In general, increased cerebrospinal fluid protein content and normal to increased cerebrospinal fluid white blood cell counts are considered the typical changes seen with brain tumors.

Meningiomas are more commonly associated with a neutrophilic pleocytosis; however, pleocytosis can be seen with other tumors as well. Choroid plexus papillomas may cause dramatic increases in cerebrospinal fluid protein concentration. Primary intracranial neoplasia is usually associated with a cerebrospinal fluid white blood cell count of fewer than 50 cells/µL with variable elevations of cerebrospinal fluid protein. In contrast, metastatic or invasive neoplasia is associated with higher white blood cell counts and protein concentrations in the cerebrospinal fluid.

Visualize it

Because most intracranial tumors are not visible with survey radiographs, computerized tomography and magnetic resonance imaging allow for localization of tumors, facilitate brain biopsy, determine the feasibility of surgical removal of a tumor, allow for a high degree of certainty about tumor type and for localization before radiation therapy, improve the owner's ability to make decisions regarding care, and enable the veterinarian to more accurately advise owners regarding therapy and prognosis.

Computerized tomographic findings for brain tumors are:

• Meningiomas are usually broad-based, peripherally located masses that were enhanced homogeneously with contrast material.

• Among the brain parenchymal tumors, astrocytomas are not distinguished easily from oligodendrogliomas because both tumors have similar tomographic features of ring-like and nonuniform enhancement, and poorly defined tumor margins.

• Choroid plexus tumors are seen as well-defined, hyperdense masses that have marked uniform contrast enhancement.

• Pituitary tumors are distinguished readily by their location, minimal peritumoral edema, uniform contrast enhancement and well-defined margins.

• In addition to defining primary brain tumors, computerized tomography may be helpful in identifying nasal tumors that have extended into the rostral cerebrum. These dogs may have no clinical signs of nasal disease. magnetic resonance imaging is optimal for demonstrating the amount of nasal or cerebral involvement and shows detailed anatomic features of these brain tumors.

Secondary tumor effects

Control of secondary tumor effects, such as increased intracranial pressure or cerebral edema, and tumor eradication (or reduction) are the primary therapy for an intracranial tumor. Palliative therapy for dogs with brain tumors consists of the administration of glucocorticoids for reducing edema, and in some cases, for retarding tumor growth.

Some animals with brain tumors demonstrate dramatic improvement in clinical signs for weeks or months with sustained glucocorticoid therapy.

Should seizure therapy be needed, phenobarbital is the drug best suited for control of generalized seizures. Eradication or reduction of a brain tumor is the primary consideration for the long-term survival of a dog with a brain tumor. Therapy for a brain tumor may include surgery, irradiation, chemotherapy, and immunotherapy (biologic response modification).

Glucocorticoids

Palliative therapy for brain tumors is administration of glucocorticoids. Glucocorticoids readily penetrate the blood-brain barrier and have some direct antitumor activity. Dexamethasone is preferred in acute and severe cases, whereas prednisone or prednisolone may be used for maintenance.

Brain tumors of any histopathologic type or location always carry a poor prognosis. Most dogs with brain tumors eventually die or are euthanized as a direct result of their tumor.