Muscle Swelling and Muscle Edema

What muscle swelling and muscle edema mean

A muscle can swell for three main reasons:

• Fluid inside the muscle (muscle edema): injured or inflamed muscle fibers leak fluid into the spaces between them.
• Bleeding into the muscle: a strain or a direct blow tears small vessels. Blood collects as a bruise or a larger hematoma.
• Inflammation or infection: immune cells and fluid flood the muscle in myositis or a bacterial infection.

Muscle edema is mainly an imaging term. On an MRI, fluid shows as a bright signal in the muscle on certain sequences. It describes what is seen, not the cause. Radiologists see it after exercise, strains, nerve injury (denervation), myositis, infection and after radiation therapy. Your doctor interprets it alongside your symptoms.

Are muscles swollen when they are sore?

Yes, slightly. After unaccustomed exercise, especially "eccentric" work such as running downhill or lowering heavy weights, muscles develop delayed onset muscle soreness (DOMS). Small fiber injuries cause mild swelling and stiffness that peak 24 to 72 hours later. The muscle can feel tight and puffy, and your range of motion is reduced. This is normal and settles in 3 to 7 days.

The "pump" during a workout is different. Blood flow and fluid shift into working muscles cause temporary swelling that fades within an hour or two.

Causes of muscle swelling

Common causes

• Exercise and DOMS: the most common cause. Both sides are usually affected and the muscle you worked is the one that hurts.
• Muscle strain (pulled muscle): sudden pain during activity, sometimes a "pop", then swelling and bruising over hours to days. Hamstrings, calves, groin and shoulders are common sites.
• Contusion (muscle bruise): a direct blow, for example a knee to the thigh in sport, causes swelling, tenderness and bruising at the point of impact.
• Overuse: repeated movements can make muscles such as the forearm or calf tight and slightly swollen.

Serious causes

• Compartment syndrome: muscles in the leg, forearm and other areas sit in tight sheaths (compartments). Bleeding or swelling raises pressure inside and cuts off blood flow. The hallmark is pain far worse than expected, pain on gently stretching the muscle, and a hard, tense limb. Acute compartment syndrome after a fracture or crush injury needs surgery within hours.
• Rhabdomyolysis: muscle breaks down and releases its contents into the blood. Causes include extreme exercise (especially in heat or when out of condition), crush injuries, long periods lying on the floor, some drugs and alcohol, and certain infections. Muscles become swollen, weak and painful and urine may turn dark brown. It can damage the kidneys. See rhabdomyolysis.
• Deep vein thrombosis (DVT): a clot in a deep leg vein causes a swollen, warm, tender calf or whole leg, usually on one side. It is not a muscle problem, but it is often mistaken for a strain.
• Infection: cellulitis spreads through the skin and soft tissue. Pyomyositis is a rarer bacterial infection inside the muscle that forms an abscess, with fever and a firm, painful swelling.

Inflammatory and other medical causes

• Myositis: autoimmune conditions such as polymyositis and dermatomyositis inflame muscles, causing weakness in the shoulders and hips, often more than pain. Viral myositis can follow flu, especially in children's calves. See myositis.
• Medicines: statins can cause muscle pain and, rarely, muscle damage with swelling. Other culprits include some antipsychotics and certain HIV medicines.
• Underactive thyroid: hypothyroidism can cause muscle aches, cramps and enlarged, stiff muscles.
• Tumors: a soft tissue sarcoma can appear as a painless, firm, enlarging lump in a muscle. It is rare, but any lump larger than about 5 cm (2 inches) or growing over weeks needs imaging.
• Myositis ossificans: after a bad thigh or arm bruise, bone can form within the muscle, leaving a firm, tender swelling that persists for weeks.

Can a muscle swell for no reason?

Usually there is a reason, even if it is not obvious. People often forget a minor knock, a new exercise or heavy lifting a few days earlier. Swelling with no injury, especially in one leg, is a reason to see a doctor, because a blood clot, infection or inflammatory condition needs to be excluded. A painless lump that keeps growing should also be checked.

Clues to the cause

Shoulder muscle swelling

Swelling over the shoulder is commonly a strained deltoid or trapezius, a bruise, or a rotator cuff injury with fluid in a nearby bursa (bursitis). Swelling after a vaccine injection is a normal local reaction that settles in 1 to 3 days. Persistent swelling, a growing lump, or swelling with fever needs a check-up.

How doctors find the cause

A doctor will ask when the swelling started, what you were doing, whether it is one-sided, about urine color, fever, new medicines and weakness. They will examine the muscle, check pulses and sensation, and compare both sides.

Tests depend on what they suspect:

• Creatine kinase (CK) blood test: high levels show muscle damage. Very high levels suggest rhabdomyolysis.
• Kidney function and urine tests if rhabdomyolysis is possible.
• Ultrasound: confirms a tear, hematoma or abscess, and a Doppler ultrasound looks for DVT.
• MRI: shows muscle edema, tears and inflammation in detail.
• Compartment pressure measurement if compartment syndrome is suspected.
• Autoantibodies and muscle biopsy for suspected myositis.

Treatment and home care

For exercise soreness, strains and bruises

• Protect and rest the muscle for the first 1 to 3 days. Avoid activities that cause sharp pain.
• Ice for 15 to 20 minutes every 2 to 3 hours in the first 48 hours. Wrap ice in a cloth.
• Compression with an elastic bandage can limit swelling. It should never cause numbness or throbbing.
• Elevation above heart level helps fluid drain.
• Pain relief: acetaminophen (paracetamol) or an NSAID such as ibuprofen. Follow the label dose. Avoid NSAIDs if you have kidney problems, stomach ulcers or take blood thinners, and avoid them if rhabdomyolysis is possible.
• Gentle movement after 2 to 3 days, then gradually return to activity as pain allows.

Do not massage or apply heat to a fresh, large thigh bruise, as this may increase bleeding and the risk of myositis ossificans.

For medical causes

Treatment targets the cause: blood thinners for DVT, antibiotics or drainage for infection, IV fluids for rhabdomyolysis, urgent surgery (fasciotomy) for compartment syndrome, and immune-suppressing medicines for myositis. If a medicine is the cause, your doctor may stop or change it.

Preventing muscle swelling

• Increase training load gradually, about 10 percent a week, especially with downhill running or heavy eccentric work.
• Warm up and build up to unfamiliar sports.
• Drink enough fluids during long or hot exercise, and stop if muscles become very painful or weak.
• Report muscle pain to your doctor if you take a statin.

Frequently asked questions

What is muscle edema?

Muscle edema means fluid has built up within a muscle. It is mostly seen on MRI and can follow exercise, a strain, a bruise, nerve damage, infection or inflammation of the muscle. It describes a finding rather than a diagnosis, so the cause depends on your symptoms and history.

Is it normal for muscles to swell after a workout?

Yes. Muscles swell briefly during exercise as blood flow increases, and mild swelling with stiffness can follow 1 to 3 days after hard or unfamiliar exercise. Severe pain, marked weakness or dark urine after exercise is not normal and needs urgent assessment for rhabdomyolysis.

How long does muscle swelling last?

Exercise soreness and mild strains usually settle in 3 to 7 days. Moderate strains and bruises can take 2 to 6 weeks. Swelling that persists beyond a few weeks, keeps growing, or forms a firm lump should be examined and may need an ultrasound or MRI.

Can dehydration cause muscle swelling?

Dehydration does not usually make muscles swell by itself. It raises the risk of cramps and, during intense exercise in heat, of rhabdomyolysis, which does cause swollen, painful, weak muscles and dark urine. Treat those symptoms as an emergency.

When is a swollen muscle an emergency?

Go to the ER if a swollen muscle is extremely painful and tense, especially after an injury, if the limb goes numb, pale or cold, if urine turns dark brown, or if a swollen leg comes with chest pain or breathlessness.

Should I use heat or ice on a swollen muscle?

Use ice for the first 48 hours after an injury, when swelling is developing. After that, gentle heat can relax stiff muscles and help movement. For exercise soreness, either can ease discomfort, and light activity usually helps more than complete rest.