CONDITION
Phaeochromocytoma
A phaeochromocytoma is a tumour that develops in the adrenal gland and releases excessive amounts of adrenaline and related hormones into the bloodstream. These hormones normally regulate heart rate, blood pressure, and the body's response to stress, but when a tumour produces them without the usual controls, the effects can appear in many different body systems at once. Owners often notice signs that seem unconnected at first—episodes of panting or restlessness, a pet that seems anxious without obvious cause, increased thirst, or changes in energy level. Some dogs show signs that come and go, while others develop patterns that persist. Because the signs can overlap with many other conditions, and because the tumour itself may be found incidentally during imaging for another reason, the path to recognising a phaeochromocytoma can vary widely. This page explores the signals that may prompt investigation, the mechanisms that link a small gland to such varied effects, the ways these tumours are identified and characterised, and the range of approaches that exist once a phaeochromocytoma is confirmed or suspected.
Why this matters now
Phaeochromocytomas tend to appear in middle-aged to older dogs, most often between eight and eleven years of age, though younger animals can occasionally be affected. There is no strong sex predisposition, but the condition has been reported more frequently in certain larger breeds. The tumour typically develops without any identifiable trigger, and many are discovered incidentally during imaging performed for another reason.
The tumour may grow slowly over months or years, and the clinical picture often evolves in a stepwise fashion rather than following a smooth trajectory. Some dogs show intermittent signs that appear during periods of stress or activity, then resolve, while others develop more persistent patterns as the tumour enlarges and hormone release becomes less regulated. The pace and character of progression can vary considerably between individuals, and in some cases the tumour remains clinically silent for an extended period.
Signals & patterns
Early signals
Episodes of panting or restlessness
An owner may notice periods where the dog pants heavily without obvious exertion, or seems unable to settle, often in the evening or after mild activity. These episodes can last minutes to hours and may occur sporadically.
Increased thirst and urination
The water bowl may need refilling more often, and the dog may ask to go outside more frequently or have accidents indoors. This pattern can develop gradually and may be mistaken for age-related change or a urinary issue.
Unexplained anxiety or agitation
The dog may appear nervous, pace without clear cause, or seek the owner's company more insistently than usual. This behaviour can come and go, and owners sometimes describe it as the dog seeming 'on edge' without an obvious stressor.
Intermittent weakness or lethargy
Some dogs show brief periods of reduced energy or reluctance to move, which may alternate with normal activity levels. These episodes can be subtle and are often noticed in retrospect once a pattern emerges.
Later signals
Persistent rapid heart rate
An owner resting a hand on the dog's chest may feel the heart beating noticeably faster than usual, even when the dog is calm. This can be present consistently rather than only during episodes.
Weight loss despite normal appetite
The dog may continue to eat well but lose body condition over weeks to months. Muscle mass may diminish, and the ribs or spine may become more prominent.
Abdominal distension or discomfort
As the tumour enlarges, the abdomen may appear fuller, or the dog may show reluctance to be touched in that area. Some dogs adopt a hunched posture or become less willing to lie on one side.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
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