What could cause small, firm, sore nodules on the fingers, specifically distal to the first knuckle, that are painful to the touch and protrude slightly?

Small Firm Nodules on Fingers: Differential Diagnosis and Management

Most Likely Diagnosis

These small, firm, tender nodules located distal to the first knuckle (proximal interphalangeal joint area) on multiple fingers most likely represent either Heberden's nodes (osteoarthritis) or digital mucous cysts, though several other important conditions must be excluded.

Primary Differential Diagnoses

Heberden's Nodes (Osteoarthritis)

• Firm bony nodules that develop at the distal interphalangeal (DIP) joints, typically affecting the 2nd, 3rd, and 4th fingers as described 1
• Can be tender, especially during active inflammation, and may appear to protrude more during inflammatory episodes 1
• More common in middle-aged women but can occur in younger individuals with genetic predisposition 1
• Associated with HLA A1, B8 haplotype in some familial cases 1
• Diagnosis confirmed by clinical examination and radiographs showing joint space narrowing and osteophytes 2

Digital Mucous Cysts

• Present as soft to firm, translucent to slightly bluish nodules near the DIP joint 3
• Can appear suddenly and may fluctuate in size, sometimes protruding more at certain times 3
• Contain clear viscous fluid and may be tender to palpation 3
• Cyst wall lacks true epithelial lining on histology, consisting of hyalinized collagen 3
• Frequently recur after drainage or conservative treatment 3

Sporotrichosis (Lymphocutaneous Pattern)

• Must be considered if there is history of trauma with thorns, splinters, or plant material 4
• Presents with subcutaneous nodules that are typically painless unless secondarily infected 4
• Characteristic proximal spread in linear pattern following lymphatic vessels 4
• Diagnosis requires culture on Sabouraud dextrose agar, which may take up to 4 weeks 4
• Treatment: Itraconazole 200 mg daily for 9-12 months (2-4 weeks after complete resolution) 4

Rheumatoid-like Nodules in Connective Tissue Disease

• Subcutaneous nodules over flexor aspects of fingers can occur in systemic lupus erythematosus 5
• Associated with arthritis, Raynaud's phenomenon, and positive ANA 5
• Histologically may resemble rheumatoid nodules despite negative rheumatoid factor 5
• Respond to hydroxychloroquine treatment 5

Critical Diagnostic Workup

Immediate Assessment Required

1. Examine for linear spread proximally along lymphatic channels - if present, strongly suggests sporotrichosis and requires culture 4
2. Assess for joint involvement - bony hard nodules at DIP joints suggest Heberden's nodes; obtain hand radiographs 1, 2
3. Check for translucency and fluctuance - if present, suggests mucous cyst; aspiration yields clear viscous fluid 3
4. Inquire about trauma history - especially thorn pricks, gardening, or outdoor activities suggesting sporotrichosis 4

Laboratory and Imaging

• Plain radiographs of affected fingers to evaluate for osteoarthritic changes at DIP joints 1
• If sporotrichosis suspected: culture aspirate or biopsy on Sabouraud agar at room temperature 4
• Consider ANA, RF, and complete blood count if systemic symptoms present 5
• Skin biopsy if diagnosis unclear - distinguishes between mucous cyst, rheumatoid-like nodule, and other pathology 3, 5

Management Algorithm

If Heberden's Nodes (Most Common)

• NSAIDs for symptomatic relief during inflammatory episodes 6
• Reassurance that condition is benign osteoarthritis
• Monitor for progression with periodic radiographs 1

If Digital Mucous Cysts

• Options include intralesional steroid injection, though recurrence is common 3
• Surgical excision provides definitive treatment but carries risk of complications 3
• Avoid simple drainage as recurrence is nearly universal 3

If Sporotrichosis Cannot Be Excluded

• Do not delay culture if any suspicion exists - inoculate specimens appropriately 4
• Initiate itraconazole 200 mg daily if high clinical suspicion while awaiting culture results 4
• Continue treatment for 2-4 weeks after complete clinical resolution to prevent relapse 4

Critical Pitfalls to Avoid

• Do not assume benign osteoarthritis without excluding infectious causes, particularly sporotrichosis in anyone with outdoor exposure 4
• Do not simply drain mucous cysts - this leads to near-certain recurrence 3
• Do not miss systemic connective tissue disease - check for associated symptoms like Raynaud's, arthritis, or constitutional symptoms 5
• If treating presumed sporotrichosis, do not stop treatment prematurely - must continue 2-4 weeks beyond clinical resolution 4

Red Flags Requiring Urgent Evaluation

• Rapid proximal spread in linear pattern - suggests lymphocutaneous infection requiring immediate culture 4
• Systemic symptoms (fever, malaise, weight loss) - consider systemic disease or disseminated infection 6, 5
• Necrosis or vascular changes - may indicate vasculitis such as cutaneous polyarteritis nodosa 7