14 Conformational Disorders
Disorders can be classified by the presenting signs. The breathing pattern can help localize the disorder. An obstructed breathing pattern is found in cases of upper and lower airway disease, while a restricted pattern indicates disease in the thoracic wall, sternum, or diaphragm. Abnormal breath sounds are common in upper airway disease. Stertor (snore) is found in nasal or pharyngeal disease and stridor (wheeze) in laryngeal or lower airway disease. A voice change and inspiratory dyspnea are often noted in the history of dogs with laryngeal disease. Patients with disease in the lower airways may present with a cough, tachypnea, or varying degrees of respiratory distress.
Conformational changes may be congenital or acquired. Acquired disease may be secondary to physical characteristics such as negative intra-airway pressure generated during inspiration in brachiocephalic airway syndrome, inflammation or infection, nasopharyngeal polyps, or diaphragmatic hernia due to trauma. Changes may be structural or functional, static or dynamic. Having this knowledge helps determine what diagnostic tests are appropriate. For example, a direct examination of the larynx is needed to make a diagnosis of laryngeal paralysis; fluoroscopy or bronchoscopy may be needed to document tracheal or bronchial compression or obstruction due to lymphadenomegaly, which cannot be entirely ruled out by examination of static thoracic radiographs.
A recent prospective study concluded that Labrador Retrievers and Rottweilers have a significantly higher risk for acquired laryngeal paralysis. Other large breeds including Irish Setters, Golden Retrievers, and Afghans, are also considered to be predisposed.
Bichon Frise, Border Collie, Bullmastiff, Chihuahua, Chinese Shar-Pei, Chow Chow, Dachshund, Dalmatian, Doberman Pinscher, English Springer Spaniel, English Pointer, English Setter, Golden Retriever, Gordon Setter, Miniature Poodle, Newfoundland, Old English Sheepdog, Rottweiler, and Staffordshire Bull Terrier are all breeds with reported cases of primary ciliary dyskinesia (PCD) or Kartagener’s syndrome. With the exception of Newfoundlands, in which PCD shows an autosomal recessive pattern of heritability, sporadically reported cases do not represent specific breed predisposition for PCD. There is a rhinitis/bronchopneumonia syndrome in Irish Wolfhounds that is not PCD and is likely heritable.
A swimmer puppy has an abnormal thoracic conformation (pectus excavatum) resulting from abnormal locomotion. Typically a puppy presents by 12 weeks of age for an inability to walk and moves around on its sternum by flailing its abducted limbs. Dorsal to ventral narrowing of the thorax develops and results in a flattened appearance. Often environmental factors such as hard slippery flooring contribute to an inability of the puppy to adduct its limbs and stand. Orthopedic abnormalities such as dislocation or subluxation of the shoulder, elbow, hip, or stifle should be ruled out. Correcting limb position and realigning joints (using hobbles to prevent abduction) typically eliminate the need for any thoracic splinting.