Differential Diagnoses for Proximal Forearm Pain
The most likely diagnosis is brachioradialis muscle pain or strain, given the dorsal/anterior-proximal forearm tenderness just distal to the elbow, pain with elbow flexion, absence of epicondylar tenderness, and partial response to NSAIDs. 1
Primary Differential Considerations
1. Brachioradialis Muscle Pain/Strain (Most Likely)
The clinical presentation strongly suggests BR muscle pathology:
- Location: The BR muscle originates from the lateral distal humerus and runs along the dorsal/anterior aspect of the proximal forearm—precisely where your patient has tenderness 1
- Mechanism: Arises from repetitive overuse, sudden overloading, or direct trauma 1
- Pain pattern: Sharp/shooting pain during activity, aching at rest, aggravated by activities requiring elbow flexion with neutral hand position 1
- Response to NSAIDs: Partial benefit from Voltaren (diclofenac) 2 is consistent with inflammatory muscle pain
Key distinguishing feature: Pain with elbow flexion (especially with neutral forearm position) but no epicondylar tenderness differentiates this from lateral epicondylitis 1
2. Radial Tunnel Syndrome
Consider this as a close second differential:
- Location: Posterior interosseous nerve compression occurs in the proximal forearm, often at the arcade of Frohse within the supinator muscle 3
- Presentation: Vague proximal forearm pain, typically 3-4 cm distal to lateral epicondyle
- Key difference: Usually presents with more diffuse aching rather than focal tenderness, and pain is often worse with resisted supination or middle finger extension 3
- Important caveat: Can coexist with lateral tendinosis, and the ECRB tendon may contribute to nerve compression 3
3. Lateral Cutaneous Nerve of Forearm (LCNF) Compression
Less likely but worth considering:
- Mechanism: Compression occurs at the antecubital fossa where the nerve lies subcutaneously 4
- Triggers: Biceps contraction with elbow extension, forearm pronation, or repetitive motion 4
- Presentation: Primarily sensory symptoms (numbness, paresthesias) along lateral forearm
- Key difference: Your patient lacks sensory complaints, making this less probable 4
4. Pronator Teres Syndrome
Lower on the differential but possible:
- Location: Median nerve compression at the elbow/proximal forearm level 5, 6
- Presentation: Volar forearm pain with median nerve paresthesias (thumb, index, middle fingers) 6
- Key difference: Tenderness is typically on the volar aspect, not dorsal/anterior as in your patient 5
Diagnostic Approach
Initial imaging per ACR guidelines: Start with plain radiographs of the elbow to exclude occult fracture, heterotopic ossification, or other bony pathology 7
If radiographs are normal or nonspecific:
- For suspected soft tissue injury (muscle, tendon, ligament): Ultrasound or MRI without contrast are equivalent appropriate options 8
- Ultrasound advantages: Can evaluate BR muscle in real-time, assess for tendon tears, and perform dynamic examination 8
- MRI advantages: Better overall soft tissue characterization if diagnosis remains unclear 8
Clinical Pearls and Pitfalls
Common pitfall: Assuming all lateral elbow/proximal forearm pain is "tennis elbow" (lateral epicondylitis). Your patient's lack of epicondylar tenderness excludes this diagnosis 1, 3
Important distinction: The BR muscle is frequently overlooked as a pain source, leading to misdiagnosis as lateral epicondylitis, radial tunnel syndrome, or even cervical radiculopathy 1
Examination maneuvers to differentiate:
- BR muscle pain: Pain with resisted elbow flexion in neutral forearm position, tenderness over muscle belly 3-5 cm distal to elbow 1
- Radial tunnel syndrome: Pain with resisted supination or resisted middle finger extension 3
- Lateral epicondylitis: Tenderness directly over lateral epicondyle, pain with resisted wrist extension 3
Response to treatment: BR muscle pain typically responds to conservative management (rest, ice, NSAIDs, stretching), which aligns with your patient's partial response to Voltaren 1