You're speaking with Dr. Michael Salkin. Welcome to JustAnswer. I'm currently typing up my reply. Please be patient. This may take a few minutes.
Marion, I'm sorry that your question wasn't answered in a timely manner. How long has it been since your Chihuahua last ate? Can you upload a copy of his test results to our conversation? I understand that you might not have a copy at home but his vet can give you one which you can scan into your computer and then give me the file link or you can photograph the pages and upload them by using the paperclip icon (if you can see that icon) or by using an external app such as dropbox.com/
I not only review the test results but also note which tests should have been performed but weren't. Does the "scan" imply X-rays, ultrasound, CT, or MRI and which parts of his body are to be scanned?
I can understand your frustration. Anorexia is one of the least specific clinical signs and will not in itself direct the clinical evaluation. Anorexia is purely an indication of underlying disease. For the truly anorexic patient, the causes may be legion. It's vital to differentiate between a patient disinterested in eating and one who experiences difficulty or discomfort while eating. Thereafter, routine laboratory tests and diagnostic imaging complement the history and physical exam for elucidating the cause of anorexia.
Here is a synopsis of the differential diagnosis for anorexia:
Disinterested in food altogether (true anorexia): systemic disease, infection/inflammation, neoplasia, food aversion
Reluctance to eat (pseudoanorexia)
Associated with pain/discomfort
Painful prehension or mastication, odynophagia (repeated attempts at swallowing) as seen with: retrobulbar abscesses from apical/tooth root abscesses, e.g., intraoral masses/foreign bodies, mandibular fractures/temporomandibular joint disease, masticatory myositis (inflammation of the muscles of chewing), periodontal disease, salivary gland disorders, oropharyngeal dysphagia, esophageal disease (masses, foreign bodies), nasal disease affecting sense of smell.
Associated with nausea
Gastrointestinal inflammatory disease, ileus (paralysis of the GI tract), delayed gastric emptying, vestibular disease, side effect of medications; many drugs have GI tract side effects.
The initial database for pseudoanorexia is a neurologic examination, oral, dental, and cranial examination (sedation or general anesthesia); radiographs of the teeth, mandible, or nasal cavity may be required. Thoracic radiographs and/or endoscopy to evaluate the esophagus and gastroesophageal sphincter for any obstruction (e.g., strictures, masses, foreign bodies) or mobility problems. The initial database for true anorexia involves laboratory testing and imaging as suggested by history and physical exam findings.