CONDITION
Pheochromocytoma in Dogs
A pheochromocytoma is a tumour that develops in specialised tissue inside the adrenal gland—a small organ that sits near the kidney and produces hormones involved in stress response and blood pressure regulation. These tumours can release surges of adrenaline and related hormones into the bloodstream, sometimes unpredictably, which may create episodes of rapid heart rate, restlessness, heavy breathing, or collapse. In other cases, the release is steadier and signs develop more gradually. Owners often arrive at this possibility after observing intermittent episodes that seem out of character—panting without obvious cause, sudden weakness, or behaviour that suggests anxiety or discomfort—sometimes with normal periods in between. The episodes can vary in intensity and frequency, and in some dogs the condition is discovered incidentally during imaging or investigation for another concern. This page explores the signs that may prompt consideration of a pheochromocytoma, what is happening inside the adrenal gland and the wider body, how the condition is investigated through blood tests and imaging, and the approaches that exist for managing it, including surgery and medical options. The course and outcome depend on factors including the size and behaviour of the tumour, whether it has spread, and the individual dog's response to treatment.
Why this matters now
Pheochromocytomas tend to appear in middle-aged to older dogs, often between eight and eleven years of age, though younger animals can occasionally be affected. No single breed carries overwhelming risk, but the condition has been noted more frequently in larger breeds and in some boxers, German shepherds, and Labrador retrievers. The tumour develops without clear environmental or nutritional triggers; it arises from chromaffin cells that are present from birth and may undergo change over time.
The course can be quite variable. Some dogs experience intermittent episodes for weeks or months before the pattern becomes clear, whilst others develop signs more steadily as hormone release becomes sustained rather than episodic. The tumour may remain confined to the adrenal gland for a period, or it may begin to invade nearby blood vessels and tissues, and in some cases cells spread to the liver, lungs, or regional lymph nodes, which influences both the signs observed and the options available.
Signals & patterns
Early signals
Episodes of panting without exertion
A dog may begin panting heavily whilst resting or in cool conditions, often with no clear trigger. The episodes can last minutes to hours and may resolve completely, leaving the dog behaving normally in between.
Restlessness or pacing
Owners sometimes notice periods where the dog seems unable to settle, moving from room to room or shifting position frequently. This restlessness may coincide with panting or occur independently, and can be mistaken for anxiety or discomfort from another cause.
Intermittent weakness or wobbliness
Some dogs show brief episodes of unsteadiness in the hindlimbs, or they may sit or lie down suddenly during activity. The weakness typically passes, and the dog may appear entirely normal within minutes or hours.
Increased heart rate noticed at rest
An owner placing a hand on the chest may feel a noticeably fast or forceful heartbeat when the dog is calm or lying down. This can be episodic, corresponding to surges of hormone release, or it may become more persistent over time.
Later signals
Collapse or loss of consciousness
In some dogs, episodes progress to sudden collapse, with or without loss of awareness. The dog may recover spontaneously after seconds to minutes, but the events can recur and may become more frequent.
Visible abdominal swelling or discomfort
As the tumour enlarges or if bleeding occurs around it, the abdomen may appear distended or the dog may show signs of discomfort when the area is touched or when moving. This can reflect the physical mass or accumulation of fluid.
Persistent lethargy or reduced appetite
Dogs may become less interested in food or play, and rest more than usual. This shift can reflect the metabolic cost of sustained hormone excess, the presence of metastatic disease, or the effects of the tumour on surrounding structures.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
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