Collapse with strenuous exercise in a young Labrador
18-month-old Labrador Retriever used as a gundog. After 10 minutes of very intense retrieving it develops a wobbly pelvic limb gait that progresses to inability to rise, without losing consciousness. Rectal temperature 41.5 °C (a healthy Labrador after the same exercise measures 41.2 °C). It recovers in 15 minutes without sequelae. Between episodes, examination, CK, glucose, ECG and Holter monitoring are normal.
What is the most likely diagnosis and how do you confirm it?
chevron_right Show answer and explanation
A. Acquired myasthenia gravis; measure acetylcholine receptor antibodies
Myasthenia causes weakness with mild exercise that improves within a minute or two of rest, often with megaoesophagus. It does not need sustained intense exercise to be triggered.
B. Exertional heatstroke, confirmed by a temperature above 41 °C
Healthy Labradors reach similar temperatures with that exercise. Heatstroke does not resolve within minutes without sequelae and usually leaves laboratory abnormalities (coagulopathy, kidney injury, high CK).
C. Labrador centronuclear myopathy; muscle biopsy and electromyography
Centronuclear myopathy starts in puppies a few months old with persistent weakness, muscle atrophy and hyporeflexia, and worsens with cold. It is not an episodic collapse with complete normality between episodes.
D. Exercise-induced collapse linked to the DNM1 gene; genetic testing
Correct. It is typical of young, highly driven Labradors: after 5–20 minutes of intense exercise, weakness of the pelvic limbs, sometimes all four, appears with preserved consciousness and recovery within minutes. It is confirmed by genetic testing (homozygous for the DNM1 mutation).
lightbulb Key takeaway
Management is to avoid the type of activity that triggers it and to stop at the first sign of abnormal gait; exceptionally an episode can be fatal. In working or gundogs with collapse, complete normality between episodes and the link with intense exertion are the main clue.
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Updated: November 1, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.