What is the differential diagnosis for hand/wrist pain starting at the 4th and 5th fingers with tenosynovitis (inflammation of the tendon sheath) and radiation up the radial aspect of the arm?

Differential Diagnosis for Hand/Wrist Pain Starting at 4th and 5th Fingers with Tenosynovitis and Radial Radiation

This clinical presentation is anatomically inconsistent and suggests ulnar neuropathy at the wrist (Guyon's canal syndrome) as the primary diagnosis, despite the described "radial" radiation being likely a mischaracterization of proximal forearm radiation. 1, 2

Primary Diagnostic Consideration

Ulnar neuropathy at the wrist is the most likely diagnosis given:

• Pain and sensory changes specifically in the 4th and 5th digits 1
• Associated tenosynovitis (which can occur with nerve compression) 2
• Activities involving repetitive or prolonged wrist extension (cycling, karate, baseball catching) increase risk 1

Key Clinical Features to Identify

• Wrist discomfort with sensory changes in the fourth and fifth digits 1
• May present with motor symptoms in addition to sensory changes 1
• Can be caused by ganglion cysts in Guyon's canal compressing the ulnar nerve 2
• Initially may be misinterpreted as flexor tenosynovitis 2

Diagnostic Workup Algorithm

Step 1: Initial Imaging

Obtain three-view wrist radiographs immediately (posteroanterior, lateral, and 45-degree semipronated oblique) to exclude fractures and assess for bony pathology 3, 4

Step 2: Advanced Imaging Based on Clinical Suspicion

For suspected ulnar neuropathy:

• MRI without IV contrast is the appropriate next study to identify soft tissue masses (ganglion cysts) or other compressive lesions 2
• MRI can accurately depict nerve compression and associated soft tissue pathology 2
• Electrodiagnostic testing identifies the area of nerve entrapment and extent of pathology 1

For suspected tenosynovitis (if primary concern):

• Ultrasound is the preferred modality for evaluating tendon abnormalities, tenosynovitis, and stenosing tenosynovitis 3
• US can diagnose flexor tendon pathology and identify thickened retinaculum or pulley constricting the osseofibrous tunnel 5
• MRI without IV contrast can also diagnose tendon abnormalities, with improved detection when IV contrast is added 3

Alternative Diagnoses to Consider

Flexor Carpi Ulnaris Tenosynovitis

• Stenosing tenosynovitis can involve multiple tendons including flexor tendons 5
• Cardinal finding on ultrasound is thickened retinaculum or pulley constricting the tendon 5

Extensor Carpi Ulnaris Tenosynovitis

• Can present with ulnar-sided wrist pain 3, 5
• Well-evaluated with ultrasound or MRI 3

TFCC (Triangular Fibrocartilage Complex) Pathology

• Presents with ulnar-sided wrist pain 4
• MRI without contrast has high accuracy for central TFCC disc lesions 4
• MR arthrography has higher sensitivity for complete and incomplete tears 4

Lunotriquetral Ligament Injury

• Causes ulnar-sided wrist pain 4
• MR arthrography has higher sensitivity than standard MRI for tears 4

Critical Anatomical Inconsistency

The described "radial aspect" radiation is anatomically inconsistent with 4th and 5th finger involvement, which follows ulnar nerve distribution. Consider:

• The radiation may actually be proximal forearm pain along the ulnar nerve distribution, not radial-sided 1, 2
• True radial-sided pain would involve the thumb, index, and middle fingers 6, 7
• Clarify the exact location of radiation with the patient

Pitfalls to Avoid

• Do not dismiss ulnar neuropathy based on the presence of tenosynovitis - these can coexist, and tenosynovitis may be the initial misdiagnosis 2
• Do not rely on imaging alone - electrodiagnostic testing is essential to confirm nerve entrapment and determine extent of pathology 1
• Do not assume all 4th and 5th finger pain is carpal tunnel syndrome - this distribution is characteristic of ulnar nerve pathology 1
• Obtain proper three-view radiographs - two views are inadequate for wrist evaluation 6