(Kiosk 2) Intra-articular Neurofibroma as a Source of Knee Pain: A Case Report

Case Diagnosis: A 59 year old male with Neurofibromatosis Type 1 (NF1) who was found to have intra-articular neurofibroma on diagnostic ultrasound of his left knee and was effectively treated with a corticosteroid injection

Case Description or Program Description: The patient arrived for evaluation of left knee pain in the setting of a recent fall. He described the pain as sharp and was able to localize the pain to his left anterior knee and thigh. He denied any specific aggravating or alleviating factors and had no previous injuries to his left knee. A physical examination of the knee was only notable for mild tenderness to palpation of the distal quadriceps tendon. The patient was initially evaluated with x-rays of his knee, which showed no evidence of osseous or bony abnormalities. Subsequent imaging consisted of an ultrasound of his left knee, which showed a mild suprapatellar effusion as well as a 3mm intra-articular solitary neurofibroma. Shortly after obtaining the ultrasound, the patient underwent corticosteroid injection to the left knee consisting of 4cc of 1% lidocaine and 40mg triamcinolone.

Setting: Sports Medicine Clinic

Assessment/Results: He returned for follow-up 3 months after receiving the corticosteroid injection and noted that his pain had improved significantly. Additionally, ambulation and transfers were easier. He returned for follow-up again 6 months after treatment and noted sustained improvements in pain and functionality at that time. Further follow-up is ongoing at this time.

Discussion (relevance): To our knowledge, there have been very few documented cases of solitary intra-articular neurofibromas. Making the diagnosis of intra-articular neurofibroma on ultrasound is unusual, and to our knowledge there have been no other cases associated with joint pain relieved by corticosteroid injection.

Conclusions: In patients with neurofibromatosis, the differential for knee pain should include intra-articular growths. As in this case, intra-articular lesions can be investigated using diagnostic ultrasound and may be effectively managed with corticosteroid injections.