Final answer:
The symptoms of limited litter box use and significant dehydration in a cat suggest an underlying condition like diabetes mellitus or diabetes insipidus. Diabetes insipidus, caused by insufficient ADH production or receptor mutation, leads to increased urination and dehydration, making it a likely suspect.
Step-by-step explanation:
The clinical presentation of a 7-year-old cat with limited use of the litter box and 10% dehydration could suggest several potential illnesses. Notably, these signs are indicative of diseases that cause increased urination and thirst, such as diabetes mellitus or diabetes insipidus. Both conditions result in excessive urination (polyuria) which leads to increased thirst (polydipsia). Diabetes mellitus involves high blood sugar levels causing the kidneys to excrete more urine to eliminate excess glucose, while diabetes insipidus is characterized by inadequate levels of antidiuretic hormone (ADH), or a resistance to it, leading to water not being reabsorbed properly by the kidneys.
In diabetes insipidus, a chronic underproduction of ADH or a mutation in the ADH receptor impairs water retention in the kidneys, resulting in significant urine output and consecutive dehydration. Thus, with the information provided and the severity of dehydration, diabetes insipidus could be the suspected disease. However, further diagnostic tests would be required to delineate the specific cause of the cat's condition.