Another kind of muscle pain is called systemic myalgia. These muscle aches are usually related to an infection, medication side effect, or underlying disease.

Infections

Certain types of infections, especially viral, may cause muscle pain. Perhaps the most common infectious cause is flu which can cause generalized aches and pains. COVID-19 is also known to cause myalgia.

Other infections that can cause muscle pain include:

• Lyme disease

• Malaria

• Dengue fever

• Rocky Mountain spotted fever

• Trichomoniasis

• Toxoplasmosis

Medications

Muscle aches are a common side effect of drugs called statins that are used to lower cholesterol. The symptom usually begins within six months of starting treatment and can take around two months to resolve once the treatment is stopped.

Other drugs that can cause muscle pain include:

-Bisphosphonates (used to treat osteoporosis)

-Aromatase inhibitors (used to prevent breast cancer recurrence)

The rapid discontinuation of antidepressants can also cause myalgia.

Fibromyalgia

Widespread muscle pain is a symptom of fibromyalgia. The pain from this chronic disorder is often described as aching, sore, stiff, burning, or throbbing.

The cause of fibromyalgia is unknown but is thought to involve genetics, mood disorders, past diseases, and chemical imbalances that cause a heightened sense of pain.

In addition to muscle pain, people with fibromyalgia often experience sleep problems, fatigue, crawling skin sensations, morning stiffness, impaired concentration, and anxiety.

Chronic Fatigue Syndrome

Chronic fatigue syndrome, also known as myalgic encephalomyelitis, is a disorder that causes overwhelming fatigue that is not improved with rest.

In addition to tiredness and malaise (the general feeling of unwellness), people with chronic fatigue syndrome commonly experience generalized muscle aches, memory problems, sore throat, and feeling dizzy when standing up.12

Chronic fatigue syndrome is closely associated with fibromyalgia, with some researchers contending that they are both parts of the same syndrome.

Polymyalgia Rheumatica

Polymyalgia rheumatica (PMR) is an inflammatory condition usually seen in adults in their 60s and 70s. PMR causes morning aches and stiffness in the shoulders, upper arms, hips, thighs, and back of the neck. Fatigue, weight loss, poor appetite, and fever may also occur.

People with PMR often complain of difficulties pulling up their socks or raising their arms above their heads to comb or wash their hair.

The cause of PMR is unknown but is thought to be the result of a combination of genetic and environmental factors.

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease that primarily affects the joints. However, RA can also cause muscle pain.

Autoimmune disorders are caused when the immune system inappropriately attacks its own cells or tissues.

Muscle pain from RA is usually felt all over the body. This differs from the joint symptoms of RA, which are typically isolated to specific joints on both sides of the body. in addition, RA can cause a low-grade fever, weight loss, and fatigue.

The cause of RA is unknown, but genetic and environmental factors are likely involved.

Lupus

Systemic lupus erythematosus (SLE), also known simply as lupus, is a chronic autoimmune disease that affects nearly every organ in the body, including the skin, brain, eyes, mouth, lungs, heart, kidneys, intestines, and joints.

Muscle aches and weakness are common in people with lupus and are often the reason why a person first seeks diagnosis and treatment. Other symptoms include fatigue, skin rashes, hair loss, headaches, joint stiffness, weight loss, and chest pain with breathing.

Inflammatory Myopathy

Inflammatory myopathies are a group of autoimmune diseases characterized by slow but progressive muscle weakness. Some people with myopathy also have muscle pain or tenderness when touched.

The term myopathy refers to disorders of the muscles of the skeleton. These include myopathies like polymyositis (which affects muscles on multiple parts of the body), dermatomyositis (which causes muscle pain and skin rash), and inclusion body myositis (which causes muscle tissues to clump abnormally).

Thyroid Disease

Hypothyroidism (an underactive thyroid gland) commonly causes muscle aches and cramps in addition to fatigue, weight gain, constipation, cold intolerance, and dry skin. Less commonly, an overactive thyroid gland (hyperthyroidism) can cause muscle cramps.

The thyroid gland is responsible for producing hormones that help regulate metabolism (the conversion of calories to energy) and numerous other body functions. When thyroid hormone levels are too low or too high, they can interfere with the transmission of nerve signals that regulate the contraction of muscles, leading to muscle pain.

Primary Adrenal Insufficiency

Addison's disease, also known as primary adrenal insufficiency, is a rare disorder that occurs when your adrenal glands do not produce enough of the hormones needed to regulate metabolism or sexual function.

Addison's disease is often related to an autoimmune disease that attacks the adrenal glands but may also be caused by injuries or tumors.

Addison's disease can cause generalized muscle pain, fatigue, nausea or vomiting, darkening of the skin, weight loss, and salt cravings. Muscle pain associated with Addison's disease is often centered around the legs and lower back.

Osteomalacia

Osteomalacia is the softening of bone due to the loss of bone minerals. It is commonly associated with a deficiency of vitamin D and calcium. It is common in older people and linked to certain diseases (like celiac disease) and medications (like anticonvulsants).

People with osteomalacia can have muscle pain from muscle spasms and cramps. They often have aching bone pain and tenderness. Osteomalacia can also increase a person's risk of bone fractures (referred to as pathologic fractures).

Depression

Depression, while a mental health condition, is commonly associated with physical symptoms such as muscle aches and joint pain. In fact, generalized aches and pains are commonly reported by people with undiagnosed or untreated depression.

While the pain may be psychogenic (related to the mind), there is evidence that the imbalance of hormones that regulate moods, such as serotonin and norepinephrine, may contribute to chronic pain symptoms.

Rhabdomyolysis

Rhabdomyolysis is a disorder in which muscle tissues begin breaking down and releasing harmful substances into the bloodstream. The classic triad of symptoms in people with rhabdomyolysis is muscle pain, muscle weakness, and dark urine.

There are many causes of rhabdomyolysis, including excessive strenuous exercise, medications, illicit drugs, heatstroke, muscle trauma, and blood clots.

If left untreated, the accumulation of toxins can lead to acute kidney failure.