Glomus Tumor of the Knee

Glomus Tumor of the Knee – The Clinical Syndrome

Glomus tumor of the knee is an uncommon cause of knee pain. It is the result of tumor formation of the glomus body, which is a neuromyoarterial apparatus whose function is to regulate peripheral blood flow in the dermis. Glomus tumors occur most commonly in the subungual region of the fingers but may also occur in areas of the body that are not richly endowed with glomus apparatus (e.g., muscle, bone, blood vessels, and nerves). Glomus tumors tend to be bluish colored, solitary, small tumors, but occasionally can become quite large.

Most patients with glomus tumor are women 30 to 50 years old. The pain associated with glomus tumor is severe, lancinating, and boring. Patients with glomus tumor exhibit the classical triad of intermittent, excruciating pain; cold intolerance; and tenderness to palpation. If the tumor is located superficially, a bluish discoloration under the skin may be visible and the patient may experience an exacerbation of pain with exposure to cold. Because of the rarity of glomus tumor in areas other than the digits, diagnosis is often delayed.

What are the Symptoms of Glomus Tumor of the Knee?

The diagnosis of glomus tumor of the knee is based primarily on three points in the patient’s clinical history: (1) excruciating pain that is localized to the area of the tumor, (2) the ability to trigger the pain by palpating the area (Love test), and (3) marked intolerance to cold (Posner cold induction test).

Hildreth test is also useful in the diagnosis of glomus tumor. It is performed by placing a tourniquet proximal to the area of suspected tumor.

As the distal area becomes ischemic, the sharp lancinating pain characteristic of glomus tumor will occur. If the tumor is superficial enough, the examiner may identify it just beneath the skin by its bluish discoloration. The patient with glomus tumor of the knee will often guard or protect the area of the tumor to avoid stimulating the pain.

How is Glomus Tumor of the Knee diagnosed?

Magnetic resonance imaging (MRI) of the affected area often reveals the actual glomus tumor and may reveal erosion or a perforating lesion of the phalanx beneath the tumor. The tumor appears as a very high and homogeneous signal on T2-weighted images.

The bony changes associated with glomus tumor of the knee also may appear on plain radiographs if a careful comparison of the corresponding contralateral knee is made. Radionuclide bone scan also may reveal localized bony destruction. If the tumor is superficial, pain may be reproduced by placing an ice pack over the affected area. Ultrasonography and color Doppler examination may help determine the cystic or solid nature of the mass and identify vascularity. Based on the patient’s clinical presentation, additional tests, including complete blood cell count, uric acid level, erythrocyte sedimentation rate, and antinuclear antibody testing, may be indicated. Electromyography is indicated if coexistent plexopathy or radiculopathy is suspected. Surgical exploration of the affected area bed often is necessary to confirm the diagnosis. Ultimately arthroscopy or arthrotomy may be required to ascertain the exact cause of the patient’s persistent knee pain.

Differential Diagnosis

The triad of localized, intermittent, lancinating excruciating pain; tenderness to palpation; and cold intolerance makes the diagnosis apparent to an astute clinician. Glomus tumor of the knee must be distinguished from other causes of localized knee pain. If a history of trauma is present, fracture, osteomyelitis, tenosynovitis, and foreign body synovitis should be considered. If the patient has no history of trauma, tumors and diseases of the glenohumeral joint and associated soft tissues should be considered. Reflex sympathetic dystrophy should be distinguishable from glomus tumor of the knee because the pain of reflex sympathetic dystrophy is less localized and is associated with distal trophic skin and nail changes and vasomotor and sudomotor abnormalities.

Treatment

The mainstay of treatment of glomus tumor is surgical removal. Medication management is uniformly disappointing. Injection of the affected area in the point of maximal tenderness may provide temporary relief of the pain of glomus tumor and blocks the Posner cold induction test response, further strengthening the diagnosis.

Complications and Pitfalls

The main complication associated with glomus tumor of the knee involves the problems associated with delayed diagnosis, mainly ongoing destruction of the bone and soft tissues adjacent to the glomus tumor. Although usually localized and well encapsulated, rarely these tumors can exhibit aggressive invasive tendencies, making complete excision of the tumor and careful follow-up mandatory.

Clinical Pearls

The diagnosis of glomus tumor of the knee is usually straightforward if the clinician identifies its unique clinical presentation. Because of the rare potential for aggressive, invasive behavior, complete excision and careful follow-up are important. 

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