A 30-year-old Caucasian gentleman presented to our emergency department with a 2-day history of severe abdominal pain, oliguria, and dark-coloured urine. He had recently participated in a weight-lifting competition, which involved intense abdominal muscle exercises. Blood test showed elevated serum creatine kinase (CK) level (93, 538 U/L) with preserved renal function.
Based on the clinical presentation, an ultrasound (US) of the abdomen was requested, which showed diffuse, well-defined hypoechoic regions within the rectus abdominis muscle, increased muscle size and minimal hyperaemia (Figure 1). No loculated fluid collection or focal hyperechogenicity was noted. This study was supplemented with a MRI of the abdomen, which confirmed isolated involvement of the rectus abdominis muscle bilaterally (Figure 2). The post-contrast fat-saturated T1-weighted sequence demonstrated heterogeneous signal hyperintensity within the rectus abdominis muscles. On the STIR sequence, there was oedema surrounding the affected muscles. The diagnosis of localised or focal, exercise-induced rhabdomyolysis (EIR) was established based on the combination of clinical features, elevated CK level and imaging findings.
Rhabdomyolysis is defined as the breakdown of striated muscle fibres with subsequent release of its intracellular components, namely myoglobin and CK, into the circulation [1]. Myoglobin is nephrotoxic, causes renal vasoconstriction, and obstruction of the renal tubules, all of which contribute to acute kidney injury (AKI) [2]. High-intensity exercises are a known cause of rhabdomyolysis with an incidence of approximately 30 per 100,000 patient-years [3].
Rhabdomyolysis is a clinical diagnosis, however, there are no fixed criteria. Generalised myalgia, swelling and dark-coloured urine (indicative of myoglobinuria) are classic features [1,2]. CK level greater than 5 times the upper limit is a common laboratory finding. Typically, CK level rises 2-12 hours following the inciting event, and peaks at day 1-3; the risk in CK level is proportional to the extent of muscle injury [1,4]. However, reportedly, CK level greater than 10 times the upper limit can also be a physiological response to exercise [3]. Hence, we lack consensus on the diagnostic CK level with values in the literature varying from >5-500 times the upper limit [1,3].
Imaging has a limited role in establishing the diagnosis of rhabdomyolysis. It is primarily used to exclude associated findings, e.g., fractures, joint dislocation, haematoma, and to rule out differential diagnoses with similar clinical presentations, e.g., necrotising fasciitis, polymyositis, pyomyositis [2]. Magnetic resonance imaging (MRI) is the imaging modality of choice used for assessing the extent of muscle injury. In the initial stages of rhabdomyolysis, the affected muscle group appears oedematous, i.e., MRI would demonstrate homogenous signal hyperintensity on both T1 and T2 weighted sequences. Eventually, myonecrosis (irreversible muscle injury) would occur, which is characteristically seen as a rim-enhancement around the affected muscle group and heterogenous signal hyperintensity on both T1-and T2-weighted sequences [2,4]. US typically shows muscle swelling with hyperechogenic (hypercontractility of muscle fibres in the acute phase) and/or hypoechogenic (oedema/inflammation of the muscle fibres) areas, architectural distortion (myonecrosis) and fluid surrounding the affected muscle group [4].
The treatment for rhabdomyolysis is dictated by its aetiology; additionally, we may need to address complications such as AKI, compartment syndrome, and/or hyperkalaemia. We treated our patient with aggressive fluid resuscitation and corrected for electrolyte abnormalities. Typically, CK levels decline by approximately 40% per day, and usually returns to baseline within a few weeks [1].
Take-Home Message / Teaching Points:
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Exercise-induced rhabdomyolysis (EIR)
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Based on the provided abdominal ultrasound and MRI images, swelling of muscle fibers and abnormal local echo/signal intensity can be observed within the bilateral rectus abdominis area.
• On ultrasound images, the involved muscle groups show local thickening and uneven echogenicity of muscle fibers. There may be regions displaying mixed high echogenicity (indicating fiber activity changes in the acute phase) or low echogenicity (edema, inflammation), suggesting disordered muscle structure.
• On MRI T1- and T2-weighted sequences, abnormal signals are noted in the rectus abdominis: early presentations often show uniform T2 hyperintensity, indicating muscle edema. In later stages, if muscle fiber necrosis occurs, more pronounced rim enhancement and mixed high signal may be seen on T1/T2 sequences, consistent with typical imaging features of rhabdomyolysis.
Combining imaging findings and clinical presentation (abdominal muscle pain, dark-colored urine, significantly elevated CK), the following diagnoses are possible:
1. Rhabdomyolysis: High-intensity exercise or trauma leads to damage of striated muscle cells, releasing CK and myoglobin, with classic clinical manifestations such as muscle pain and tea-colored urine. Imaging can show muscle edema and necrosis.
2. Polymyositis or Dermatomyositis: These also present with elevated CK and inflammatory changes in muscle, but they usually have a longer course and other systemic manifestations (e.g., joint pain, rash). MRI often shows symmetrical muscle inflammation.
3. Wound or Infectious Lesions (e.g., Pyomyositis, Necrotizing Fasciitis): These typically come with evident signs of infection (redness, warmth, pain, fever, elevated white blood cell count), requiring further clinical correlation with blood tests and inflammatory/infectious markers.
Considering the patient’s onset after strenuous exercise, extremely elevated CK, and dark urine, exercise-induced rhabdomyolysis remains the most likely diagnosis.
Taking into account that the patient is 30 years old, developed acute abdominal pain, muscle weakness, and dark urine after a recent high-intensity weightlifting competition, and has laboratory findings (CK 90,000+ U/L) along with imaging evidence of rectus abdominis swelling and edema signals, the most appropriate diagnosis is: Exercise-induced Rhabdomyolysis.
1. Treatment Strategies:
• Aggressive Hydration: Maintain adequate blood volume through intravenous infusions to promote renal perfusion, facilitate myoglobin excretion, and prevent acute kidney injury.
• Electrolyte Balance and Management of Complications: Monitor and correct hyperkalemia, acid-base imbalances, etc.
• Observation of Muscle Injury Extent: Regular re-checks of CK and renal function indicators; adjust treatment intensity based on the decline in values and improvement of clinical symptoms.
• Other Supportive Care: Includes pain management and avoiding activities that could cause further muscle damage or complications.
2. Rehabilitation and Exercise Prescription Recommendations:
• Rest and Gradual Recovery in the Acute Phase: During the acute phase, bed rest or reduced abdominal muscle load is recommended to avoid further muscle damage.
• Exercise Frequency, Intensity, Time, Type, and Progression (FITT-VP Principle):
- Frequency: After acute symptoms subside, engage in light-to-moderate training 2–3 times per week.
- Intensity: Begin with very low intensity (e.g., simple stretching and basic core exercises), gradually increasing as tolerated.
- Time: Each session should initially last 20–30 minutes, and can be gradually extended to 45 minutes as recovery progresses.
- Type: Start with low-impact aerobic activities (e.g., brisk walking, swimming) and light-load resistance training (elastic bands or low-weight machines); avoid heavy or high-intensity abdominal exercises in the short term.
- Progression: Assess CK levels and symptom relief every 1–2 weeks before increasing training intensity or frequency.
• Individualized Assessment: If the patient has comorbidities (e.g., hypertension, diabetes) or limited cardiopulmonary function, a more comprehensive risk assessment should be conducted prior to exercise, and rehabilitation should be guided by professionals.
• Safety Monitoring: Throughout the training process, monitor local muscle soreness, systemic symptoms, and changes in urine color. If abnormalities occur, seek medical attention or adjust the plan promptly.
This report is a reference analysis based on existing case history, imaging data, and standard medical knowledge. It cannot replace in-person consultations or individualized medical advice from professionals. If the patient experiences any doubts or changes in symptoms, they should promptly seek further evaluation and treatment at a qualified medical institution.
Exercise-induced rhabdomyolysis (EIR)
