The appearance of purple discoloration on the knees can be a cause for concern. While this phenomenon can sometimes indicate an underlying health condition, it is frequently attributed to benign and temporary factors. Understanding the various reasons behind this discoloration can help in determining when medical attention is appropriate.
Common Explanations for Purple Knees
Cold Exposure
When the body is cold, blood vessels constrict to conserve heat, reducing blood flow to the skin. This decreased blood flow results in less oxygenated blood near the surface, causing the skin to appear blue or purple. The discoloration resolves as the body warms up and normal blood flow resumes.
Dependent Livedo Reticularis
Dependent livedo reticularis presents as a common skin pattern characterized by a net-like or mottled purplish discoloration. This pattern becomes more noticeable when limbs are cold or in a dependent position. It occurs due to changes in small blood vessels, where some constrict while others dilate, creating the characteristic marbling effect. This condition disappears with warmth or a change in body position.
Bruising
Bruising is a frequent cause of purple knees, resulting from trauma or injury. When small blood vessels beneath the skin are damaged, blood leaks out and pools. Initially, a bruise may appear reddish or purplish, and as the body breaks down the pooled blood, the color changes to shades of blue, black, green, or yellow. Bruises are accompanied by pain or tenderness in the affected area.
Prolonged Standing or Sitting
Prolonged standing or sitting contributes to purple discoloration due to gravity’s effects on blood circulation. When the legs remain in a dependent position, blood can pool in the lower extremities, increasing pressure within the veins. This pooling, known as venous congestion, slows blood return to the heart, causing the skin to appear discolored. Elevating the legs helps alleviate this discoloration by improving blood flow.
Underlying Medical Causes
Peripheral Artery Disease (PAD)
Peripheral Artery Disease (PAD) can cause knees and lower legs to turn purple due to narrowed arteries restricting blood flow. Plaque buildup reduces oxygen-rich blood supply to the extremities. Other symptoms associated with PAD include leg pain, numbness, coolness of the skin, or skin that appears shiny or dry.
Raynaud’s Phenomenon
Raynaud’s phenomenon involves a temporary narrowing of blood vessels in response to cold temperatures or stress. This condition can cause affected areas to change color in sequence from white, to blue or purple, and then to red as blood flow returns. The discoloration is accompanied by coldness, numbness, or tingling.
Deep Vein Thrombosis (DVT)
Deep Vein Thrombosis (DVT) is a serious condition where a blood clot forms in a deep vein. This clot obstructs blood flow, leading to symptoms: swelling, pain or tenderness, and warmth in the affected leg. The skin over the clot may appear reddish or bluish, and this condition requires immediate medical attention.
Vasculitis
Vasculitis involves inflammation of the blood vessels, leading to skin changes like purplish spots or discoloration. The appearance can range from small, reddish-purple spots (purpura) to larger blotches. Other symptoms include joint pain, muscle aches, fever, or fatigue.
Acrocyanosis
Acrocyanosis is characterized by a persistent bluish or purplish discoloration of the extremities due to the constriction of small blood vessels. Unlike Raynaud’s, the discoloration is painless and does not involve color changes from white to red. It is exacerbated by cold exposure and accompanied by cold, clammy skin.
Certain Medications
Certain medications cause skin discoloration as a side effect. Some drugs, such as NSAIDs, antimalarials, amiodarone, and tetracyclines, change skin pigmentation. The discoloration can vary in color.
When to Seek Medical Advice
Seek medical advice if purple discoloration on your knees is persistent or does not resolve with warmth or position changes. Discoloration accompanied by pain, swelling, tenderness, warmth, numbness, tingling, or weakness warrants prompt evaluation. These combined symptoms indicate a blood clot or other serious circulatory issue.
Skin changes like ulcers, sores, or shiny/dry texture also suggest medical consultation. Systemic symptoms such as shortness of breath, chest pain, or dizziness, especially with leg discoloration, require immediate medical attention.
Diagnosis and Management
When seeking medical advice for purple knees, a healthcare professional will begin with a medical history and physical exam. They will ask about the onset and duration of the discoloration, any associated symptoms, and your overall health. The physical exam assesses color, temperature, swelling, and any skin changes.
To determine the underlying cause, diagnostic tests may be ordered. Blood tests check for inflammation, clotting issues, or other systemic conditions. Imaging studies, such as an ultrasound, assess blood flow and detect clots. In some cases, advanced imaging like CT or MRI scans may be necessary to visualize blood vessels and identify issues.
Management of purple knees depends on the diagnosis of the underlying cause. For benign conditions, lifestyle adjustments (elevating legs, staying active, or using compression stockings) are recommended. If a medical condition is identified, treatment involves medication like blood thinners for DVT or specific drugs to manage conditions like Raynaud’s or vasculitis. In rare instances of severe blockages, procedures or surgery are necessary to restore proper circulation.