What is the cause of paresthesia or a thickened sensory feel in the dorsal surface of the forearm, without edema or wound, in a patient with a history of needle injury at the site?

Paresthesia and Thickened Sensory Feel on Dorsal Forearm Following Needle Injury

Most Likely Diagnosis: Post-Injection Peripheral Nerve Injury

The paresthesia and altered sensation on the dorsal forearm following needle injury most likely represents direct traumatic injury to the superficial branch of the radial nerve or lateral antebrachial cutaneous nerve, which are vulnerable to needle trauma in this anatomical region. 1

Immediate Diagnostic Approach

Clinical Localization

• Dorsal forearm paresthesia without edema or wound indicates a pure sensory nerve injury, distinguishing this from more extensive soft tissue trauma 2
• The superficial radial nerve provides sensation to the dorsal-radial hand and distal forearm, while the lateral antebrachial cutaneous nerve (terminal branch of musculocutaneous) supplies the lateral forearm 3
• The "thickened" sensory quality suggests nerve irritation or partial injury with abnormal sensory processing along the damaged nerve pathway 2

Required Diagnostic Studies

• High-resolution ultrasound of the affected nerve from the injection site distally should be obtained to identify nerve swelling, hypoechogenicity, or intraneural vascularity 1, 4
• If ultrasound is equivocal, MRI with dedicated neurography sequences provides superior soft-tissue detail for visualizing the injured nerve 1
• Nerve conduction studies may be normal early after injury or with pure small fiber involvement, but can help confirm the diagnosis if performed 3-4 weeks post-injury 3

Management Algorithm

First-Line Treatment (Immediate)

• Topical NSAIDs should be applied to the injection site for localized pain and inflammation 1
• Avoid repeat trauma to the area and any activities that stretch or compress the affected nerve 3

Pharmacologic Management for Neuropathic Symptoms

• If paresthesias are bothersome, duloxetine is the first-line pharmacologic treatment for peripheral neuropathy with numbness and tingling 5
• Oral pregabalin can be considered as an alternative, particularly if there is significant neuropathic pain 6
• Acetaminophen or NSAIDs may be offered for associated pain 5

Interventional Options

• Ultrasound-guided perineural steroid injection can be considered if symptoms persist beyond 2-4 weeks 6
• This approach showed >80% resolution of sensory symptoms at 1-month follow-up in documented cases of traumatic nerve injury 6

Expected Clinical Course

Prognosis

• Most post-injection neuropathies resolve spontaneously within weeks to months with conservative management 6
• Complete return of sensation typically occurs within 3-14 months depending on injury severity 7
• Persistent symptoms beyond 3 months warrant repeat imaging and consideration for specialist referral 3

Critical Red Flags to Exclude

When to Suspect Alternative Diagnoses

• Bilateral hand involvement would suggest cervical cord pathology (C5-C7 level) rather than isolated peripheral nerve injury 8
• Rapidly progressive weakness, areflexia, or ascending paresthesias require urgent evaluation for Guillain-Barré syndrome 8
• Burning dysesthesias in both forearms with hand weakness suggests central cord syndrome requiring urgent MRI 5, 8
• Compression by space-occupying lesion (lipoma, ganglion) should be considered if symptoms progressively worsen despite conservative treatment 7

Common Pitfalls to Avoid

• Do not assume symptoms will resolve without documentation of the injury and baseline assessment - obtain ultrasound early to establish diagnosis and guide treatment 1
• Do not delay imaging if symptoms are atypical or non-improving after 4 weeks - underlying structural causes like tumors can present similarly 7
• Do not overlook systemic causes - check for diabetes, vitamin B12 deficiency, thyroid dysfunction, or other metabolic causes if symptoms are bilateral or out of proportion to the injury 5, 3
• Massage therapy or aggressive physical manipulation of the area should be avoided as this can worsen nerve injury 6