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unilateral leg swelling Post-Thrombotic-Syndrome

Unilateral leg swelling: Post-Thrombotic Syndrome vs Lymphedema

Last Updated: March 12, 2023 | Dr Reza Moazzeni

According to medical research, the primary conditions responsible for causing swollen legs on one side are venous stasis (such as Deep Vein Thrombosis (DVT) or venous insufficiency), lymphedema, malignancy, trauma and infections (such as cellulitis). Categorizing the swelling as either acute or chronic can help to streamline the diagnostic process. In this context, I present two cases that utilize a simplified approach to diagnosing the cause of unilateral swelling of the lower extremities.

Case 1

A 78-year-old man has been experiencing skin discolouration and thickening on his left leg for many years, accompanied by mild swelling and a dull chronic ache, which he has grown accustomed to. His symptoms have been present for over ten years and are considered chronic. The presence of hyperpigmentation (darkening of the skin), lipo-dermatosclerosis and eczema, mainly on the left side, suggests a venous source of the problem and indicates the chronicity of the condition, as shown in the pictures below.

The patient’s medical history revealed a past occurrence of Deep Venous Thrombosis (DVT) twelve years before the current presentation. The DVT was severe and required one month of hospitalization and full anticoagulation therapy, as can be observed in the pictures below. The patient also had a few venous ulcers, which have since healed.

Post-Thrombotic Syndrome (PTS) is a condition that can occur following a deep vein thrombosis (DVT), where blood clots form in the deep veins of the legs. PTS can develop if the veins are damaged during a DVT, which can cause blood to pool in the legs. After an episode of acute DVT, Post-Thrombotic Syndrome or Venous Stasis Syndrome (VSS) is known to occur in approximately 30-40% of cases, to varying degrees. In approximately 4% of patients, the symptoms can be severe. Typically, symptoms manifest within the first six months following the acute event, but it is rare for PTS to develop after two years. Common symptoms associated with PTS include:

  • Chronic pain and diffuse aches
  • Skin discoloration (Hyperpigmentation)
  • Skin dryness and eczema
  • Hardening of the skin (Lipodermatosclerosis)
  •  Skin ulcers
In this particular case, the patient experienced a mild form of Post-Thrombotic Syndrome following an episode of DVT. As the symptoms had been present for several years and were relatively mild, the patient did not seek specific therapy. Nonetheless, this case serves as a reminder to healthcare professionals to consider Post-Thrombotic Syndrome when presented with complaints of unilateral limb swelling. In order to uncover relevant medical history, it is important to make specific inquiries about prior episodes of DVT, hospitalization, or anticoagulation, as patients may not recall such events over time.

Case 2

The second case involves a 75-year-old man who was referred for investigation of his swollen right leg. Although he had been diagnosed with Neuroendocrine Tumor, which required chemotherapy and surgery, his swollen right leg raised concerns of Heart Failure. Images depicting the leg are shown below. (Click to enlarge)

The images indicate that there are no signs of venous stasis in this particular case, as evidenced by the absence of hyperpigmentation and lipodermatosclerosis. Additionally, an echocardiogram did not reveal any evidence of heart failure, which is not typically associated with unilateral leg edema. Furthermore, there was no lymphadenopathy or mass effect that could explain the patient’s unilateral lymphedema. 

Upon further questioning, it was discovered that the patient had been experiencing this unilateral leg swelling for over 40 years. The language barrier had caused confusion among his treating oncologists. At 30 years old, he had been involved in a severe motor vehicle accident that resulted in multiple fractures in his right leg. He had to keep his leg in a cast for almost a year. Subsequently, his unilateral leg swelling slowly emerged and never resolved. This is a case of traumatic lymphadenopathy, which can only be diagnosed through a comprehensive history and the exclusion of other potentially serious causes.


Both cases presented with chronic unilateral leg swelling; however, there are notable differences between them. The first case displays clear indicators of chronic venous stasis, such as significant skin thickening and hyperpigmentation, while the second case, despite having significant pitting edema, shows intact skin texture with no hyperpigmentation or lipodermatosclerosis. Establishing the timeline of the swelling is an essential initial step in diagnosing unilateral leg swelling.

Acute unilateral leg edema is commonly caused by infectious (cellulitis) and vascular (Deep Vein Thrombosis) conditions. Cancer and mass effects resulting from compression of large femoral or iliac veins can also be an uncommon cause of acute unilateral leg swelling. Lymphoma, for instance, can cause unilateral lower extremity edema and necessitates a high index of suspicion for timely diagnosis.

Chronic causes of unilateral lower leg swelling include post-thrombotic syndrome and secondary (traumatic) lymphedema. A patient can develop traumatic lymphedema either due to lymph node removal as a part of cancer treatment or permanent damage to the lymphatic system during severe limb injuries.