What illness starts with achy legs?

According to UCLA Health, body aches are a common symptom when the immune system responds to an infection, causing inflammation in the muscles. For many, the first sign of an infection like the flu or COVID-19 can be persistent muscle pain, including those in the legs, which can lead to questions about what illness starts with achy legs.

Quick Summary

Achy legs can be an early symptom of common viral infections, including the flu, COVID-19, and other causes like the common cold, as the body's immune system fights inflammation. Less commonly, persistent or unexplained achiness may indicate underlying issues such as peripheral artery disease (PAD), deep vein thrombosis (DVT), or an autoimmune disorder.

Key Points

• Viral Infections Cause Myalgia: Common viruses like the flu, COVID-19, and the common cold cause widespread muscle aches (myalgia) as a result of the body's immune and inflammatory response.

• PAD Causes Aches with Activity: Peripheral Artery Disease (PAD) is a circulatory issue that causes leg pain (claudication) during exercise, which subsides with rest, and is due to narrowed arteries.

• DVT is a Serious Concern: Deep Vein Thrombosis (DVT), a blood clot in the leg, can cause achy legs along with swelling, redness, and warmth, and requires immediate medical attention.

• Autoimmune Disorders Create Chronic Pain: Conditions like fibromyalgia, lupus, and rheumatoid arthritis can lead to chronic, widespread muscle and joint pain, including achy legs.

• Dehydration and Medication are Factors: Dehydration and certain medications (like statins) can also contribute to muscle aches and cramps.

• Know When to See a Doctor: Persistent, severe, or unexplained leg pain, especially when accompanied by swelling, fever, or difficulty walking, should be evaluated by a healthcare professional.

Common Viral Infections

Achy legs are a frequent early indicator of viral infections, occurring as the body's immune system mounts a defense. This response releases white blood cells that cause widespread inflammation, often resulting in muscle aches known as myalgia. This discomfort is a sign that your immune system is hard at work.

The Flu (Influenza)

The flu is one of the most common illnesses known to begin with significant body aches, particularly in the back and legs. These muscle aches, or myalgia, are often accompanied by other symptoms such as fever, fatigue, weakness, and chills. The discomfort typically peaks within the first few days and subsides as the viral infection runs its course. Hydration and rest are crucial for recovery during this period.

COVID-19

In a similar vein to the flu, COVID-19 can also start with muscle and body aches. While the virus manifests differently in various individuals, achy legs are a potential early sign. The underlying cause is the body's inflammatory response to the SARS-CoV-2 virus. In more severe cases, some patients may experience myositis, an inflammation of the muscles.

Other Viral Illnesses

Several other viral infections can also trigger myalgia at the onset. These include:

• Common Cold: Although typically milder than the flu, a common cold can still cause slight muscle aches as the immune system fights the infection.
• Mononucleosis (Mono): This viral infection, caused by the Epstein-Barr virus, is known for causing severe fatigue and body aches.
• Leptospirosis: A bacterial infection transmitted through contaminated water, leptospirosis can cause severe muscle aches, fever, and headaches.

Blood Flow and Circulatory Issues

Beyond infections, several conditions related to blood flow can manifest with achy legs as an early symptom. These often require medical attention to prevent serious complications.

Peripheral Artery Disease (PAD)

PAD is a vascular condition where arteries in the limbs, most commonly the legs, become narrowed due to plaque buildup. This limited blood flow causes a type of leg discomfort called claudication, which typically begins during physical activity and subsides with rest. The pain can feel like aching, cramping, or a feeling of heaviness in the leg muscles. As the condition progresses, pain may even occur at rest.

Deep Vein Thrombosis (DVT)

A deep vein thrombosis is a blood clot that forms in a deep vein, usually in the lower leg or thigh. A DVT can present with pain, swelling, redness, and warmth in the affected leg. In some cases, there may be no initial symptoms, but if it travels to the lungs, it can become life-threatening. Calf pain after sitting for extended periods is a potential warning sign.

Autoimmune and Inflammatory Disorders

Chronic pain, including achy legs, can also be a hallmark of certain autoimmune and inflammatory conditions where the immune system mistakenly attacks healthy tissues.

Fibromyalgia

Fibromyalgia is a chronic condition characterized by widespread pain and stiffness throughout the body, including the legs. The pain is often accompanied by fatigue, sleep problems, and mood issues. The exact cause is unknown, but it is believed to involve a mix of genetic and environmental factors.

Lupus

Systemic lupus erythematosus (SLE), commonly known as lupus, is an autoimmune disease where the body attacks its own tissues. This inflammation can cause joint pain and arthritis, which can feel like achy legs.

Rheumatoid Arthritis (RA)

RA is another autoimmune disease that causes inflammation in the joints, leading to pain and stiffness. While it typically affects multiple joints, including those in the legs, it can start with general achiness.

Other Considerations

Pinpointing the exact cause of achy legs is not always straightforward, as numerous factors can contribute.

The Role of Dehydration and Electrolytes

Dehydration can lead to muscle cramps and aches because water is essential for normal muscle function. Low levels of electrolytes like potassium can also result in muscle cramps and weakness. When you are sick with a fever or flu, the risk of dehydration is higher, exacerbating muscle aches.

Medication Side Effects

Certain medications can have side effects that include muscle aches and pain. Statins, which are used to lower cholesterol, are a well-known example. If you suspect a new medication is causing your symptoms, it is important to speak with your doctor.

When to Seek Medical Attention

While many causes of achy legs resolve on their own, certain red flags should prompt a visit to a healthcare provider. You should seek medical help if you experience any of the following:

• Severe pain that comes on suddenly
• Swelling, redness, or warmth in one leg
• Fever along with the leg pain
• Pain that doesn't improve with rest and home care
• Calf pain after a long period of sitting
• Difficulty walking or bearing weight on the leg
• Shortness of breath or chest pain (this is a medical emergency)

Comparative Table of Illnesses with Achy Legs

Symptom Profile	Common Viral Infections	Peripheral Artery Disease (PAD)	Deep Vein Thrombosis (DVT)	Fibromyalgia	Autoimmune Conditions
Onset	Often acute, with other symptoms like fever.	Typically gradual, worsening over time.	Can be sudden, often in one leg.	Chronic and widespread, not tied to a specific illness.	Can be chronic, with waxing and waning symptoms.
Associated Symptoms	Fever, fatigue, chills, sore throat, cough.	Leg numbness, heaviness, coldness, slow-healing sores.	Swelling, redness, warmth, tenderness in one leg.	Fatigue, sleep issues, cognitive difficulties, sensitivity to pain.	Joint pain, fatigue, rashes, and other systemic symptoms.
Effect of Activity/Rest	Aches often worse during the acute phase of illness; improve with rest.	Aches typically occur during activity (claudication) and improve with rest.	Pain is constant and may worsen with movement.	Pain is often persistent and not consistently affected by rest or activity.	Pain can worsen with activity but is not always consistent.
Primary Cause	Immune system's inflammatory response to a virus.	Plaque buildup narrowing arteries.	Blood clot formation in a deep vein.	Brain processing of pain signals, often with other factors.	Immune system attacking the body's own tissues.

Conclusion

While achy legs often accompany common illnesses like the flu, serving as a signal that your immune system is active, persistent or unusual leg pain warrants attention. Conditions like peripheral artery disease, deep vein thrombosis, and autoimmune disorders can all begin with aching legs but require a different approach to diagnosis and treatment. Paying attention to accompanying symptoms, such as fever, swelling, or pain that worsens with rest, can help determine the underlying cause. Always consult a healthcare professional for a proper diagnosis, especially if your symptoms are severe or persistent. For more information on health conditions and when to seek medical help, please visit the Mayo Clinic website.

Frequently Asked Questions

Why do viral infections cause my legs to ache?

When you have a viral infection like the flu or COVID-19, your body's immune system releases inflammatory chemicals called cytokines to fight the infection. This inflammatory response can cause myalgia, or muscle pain, throughout the body, including the legs.

Can achy legs be a sign of something serious?

Yes, while often a sign of a minor illness, achy legs can indicate a serious condition. Pay close attention if the pain is severe, accompanied by swelling, redness, or warmth in one leg, as this could signal a deep vein thrombosis (DVT).

What is the difference between achy legs from the flu and from PAD?

Achy legs from the flu are caused by your body's immune response to an infection and are typically associated with fever and fatigue. Achy legs from Peripheral Artery Disease (PAD) are caused by poor blood flow and characteristically occur with physical activity, such as walking, and improve with rest.

Could my medication cause my legs to ache?

Yes, certain medications, particularly cholesterol-lowering statins, can cause muscle pain and weakness as a side effect. If you've started a new medication and developed achy legs, it's a good idea to speak with your doctor.

How can I tell if my achy legs are from dehydration?

Achy legs from dehydration are often accompanied by muscle cramps. If you've been sick with symptoms like fever, sweating, or vomiting, you may be dehydrated. Increasing your fluid intake can help determine if dehydration is the cause.

When should I see a doctor for achy legs?

You should see a doctor if your achy legs are severe, persistent, or worsen over time. Immediate medical attention is needed if you also experience swelling, redness, warmth in one leg, or shortness of breath and chest pain.

Can achy legs be a symptom of a chronic condition?

Yes, chronic conditions such as fibromyalgia and autoimmune disorders like lupus can cause persistent and widespread muscle and joint pain, including achy legs.