A 16-year-old boy with lower extremity muscle wasting and pain

CASE DESCRIPTION

A 16-year-old boy presented with 1-year history of left thigh pain that was dull in nature and lasted for several hours every day with minimal response to multiple analgesics (non steroid anti-inflammatory drugs, Acetaminophen, and Pregabalin). He denied any back discomfort, incontinence, muscle cramps, falling incidents, or sensory symptoms. There was no relevant past medical or family history.

On physical examination, there was obvious wasting of the left lower extremity. Left mid-thigh circumference measured 42 cm as compared to right side 45.5 cm. And left calf measured 32 cm in comparison to right calf 35 cm (Figure 1). Deep tendon reflexes were +2 bilaterally with normal plantar responses. There was no evidence of increased tone. He had subtle weakness in left hip abduction/adduction and knee extension. The sensory exam was normal. Straight leg raise tests were both negative and there was no pain to palpation.

Figure 1. .

Inspection revealed muscle wasting in Vastus Lateralis, Rectus Femoris, Vastus Medialis, and medial Gastrocnemius.

The following radiologic images were done in order over a period of 6 months, X-rays knee and femur, MR spine, MR pelvis and thigh and MR head did not show any evidence of muscle, bone, vascular, lumbosacral plexus injury, or nerve lesion. Then, Doppler ultrasound for leg vessels was done and reported normal. Nerve conduction and electromyography studies were repeated twice over the same period and came back normal. After these extensive investigations and consultation with multiple specialists, a final imaging study and procedure revealed the diagnosis.

CASE FORMULATION AND DISCUSSION

A CT knee showed a proximal tibial lesion. Thus, he underwent biopsy and radio-frequency ablation and a benign Osteoid Osteoma (OO) was detected (Figure 2).

Figure 2. .

6 mm diameter geographic round predominantly cortically dense and mixed osteo sclerotic-osteolucent focus of bone within the central medullary portion of the proximal tibial epiphysis at the level of the physis without demonstration of surrounding hypertrophic bone formation.

OO is a benign bone tumor which affects males more commonly than females, and while it can present at any age its peak incidence is in the late teens or early adulthood. The tumor can occur in essentially any bone, but is most commonly localized in the femur and tibia. It can present initially with significant pain, which often involves a wider distribution than the location of the lesion itself, making localization challenging (1). Radiographic changes on initial plain x-ray are often absent or subtle frequently leading to a delay in the diagnosis (2). In addition to these misleading features, neurological signs and symptoms can be seen in up to 30% of the cases and often prompt extensive investigation of the spine and neuromuscular system in search for neurological explanations (1). CT scan is the most sensitive and specific imaging modality.

The neurologic manifestations of OO were originally described back in 1990 by Kiers et al. who evaluated retrospectively 38 patients diagnosed with this neoplasm (1). It was not uncommon that referred pain was the initial presentation followed by muscle atrophy of the affected extremity, weakness, and ataxic gait and that this mostly precedes any radiologic proof of the lesion (1). Also, Schulman et al. explained the radicular pain associated with OO, providing evidence that it is a highly vascular lesion that can have autonomic nerve fibers within its nidus which are spinal in origin giving the picture of referred pain. In addition, oedema surrounding the neoplasm can compress nearby nerve fibers thus triggering them and accounting for localized pain (3). Other case reports describe similar spectrum of neurologic manifestations of OO (2). The pathophysiology for these conspicuous neurologic findings is still vague, and the symptoms can be dramatic making the diagnosis a particular challenge in many cases.

Following radio-ablation of the OO, our patient had complete and immediate resolution of his pain and is back to regular activities. We will continue to follow the trajectory of his muscle wasting, which presumably will take a much longer time to resolve.

In summary, OO can have pain characteristics and neurologic signs that frequently confound the diagnostic effort, and combined with the fact that radiographs can be normal early on in the course of the disease, the diagnosis can be challenging. Radicular and nonspecific pain is one of the early and remarkable symptoms and can be resistant to analgesics as time progresses. Therefore, physicians should have an awareness of OO and a high index of suspicion for this benign neoplasm in scenarios of pain and muscle wasting. The condition is curable and pain remits once the OO lesion is managed.

CLINICAL PEARLS

• OO, a benign bone lesion, can present with neurologic symptoms that may be misleading

• OO pain can be poorly localized, radicular, intense, more constant with time and have suboptimal response to analgesics.

• A high index of suspicion for OO is important to ensure prompt diagnosis given it can be effectively treated and CT scan is the most sensitive and specific imaging modality

INFORMED CONSENT

Informed consent for publication of this case was obtained from the patient.

FUNDING

There are no funders to report.

POTENTIAL CONFLICTS OF INTEREST

TC reports honoraria received from Biocomposites Inc. for presentations given in May 2021. There are no other disclosures. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.