Differential Diagnoses for Subungual Hematoma of the Toenail
When evaluating a suspected subungual hematoma of the toenail, you must critically distinguish it from subungual malignant melanoma, which is the most life-threatening mimic, along with other infectious and non-infectious nail dystrophies that can present with similar discoloration.
Critical Life-Threatening Differential
Subungual Malignant Melanoma
- This is your cannot-miss diagnosis - the most important differential from a mortality standpoint 1
- Unlike true hematoma, melanoma will not grow out with the nail over time
- Requires biopsy if there is any diagnostic uncertainty
- Particularly concerning if there is no clear history of trauma
Infectious Differentials
Fungal Infections (Onychomycosis)
The British Association of Dermatologists guidelines identify several fungal patterns that can mimic subungual hematoma through nail discoloration 1:
Dermatophyte infections:
- Distal and lateral subungual onychomycosis (DLSO) - causes thickening and discoloration, most common pattern
- Superficial white onychomycosis - white lesions on nail surface
- Total dystrophic onychomycosis - complete nail destruction with discoloration
Key distinguishing features: Fungal infections typically produce soft, friable nail surfaces, whereas trauma/hematoma maintains nail plate integrity 1
Candidal Onychomycosis
- Usually begins proximally with associated paronychia 1
- Less likely to mimic subungual hematoma pattern
- More common in immunocompromised patients
Mould Infections
- Account for 5% of onychomycosis in the UK 1
- Often affect previously traumatized nails, which can confuse the clinical picture 1
Bacterial Infection
Pseudomonas aeruginosa specifically causes green or black nail discoloration that can mimic hematoma 1
- Key differentiator: bacterial infections can coexist with trauma
Non-Infectious Differentials
Chronic Repetitive Trauma
- This is the most common benign mimic 1
- Results in distal onycholysis and nail discoloration
- Critical diagnostic maneuver: Clip the affected nail area and examine the nail bed - it will appear normal with intact longitudinal epidermal ridges if trauma is the cause rather than infection 1
Psoriasis
- Can cause subungual hyperkeratosis and discoloration 1
- Look for other nail signs: pitting, oil spots, onycholysis
- May have secondary candidal infection 1
Lichen Planus
- Affects approximately 10% of patients with lichen planus 1
- Associated findings: nail plate thinning, subungual hyperkeratosis, dorsal pterygium
- Look for oral or cutaneous lesions
Other Dystrophic Conditions
Less common mimics include 1:
- Onychogryphosis - thickened, curved nails
- Darier disease
- Yellow nail syndrome - light green-yellowish pigmentation with hardness and elevated longitudinal curvature
- Ichthyotic conditions
Diagnostic Approach Algorithm
First: Establish trauma history
- Clear recent trauma → likely true hematoma
- No trauma or chronic presentation → proceed with differential workup
Second: Examine nail characteristics
- Soft, friable surface → fungal infection likely
- Hard, intact plate → consider melanoma, trauma, or other causes
- Green/black color → consider Pseudomonas
Third: Perform nail bed examination
- Clip affected nail and inspect bed
- Normal bed with intact ridges → trauma
- Abnormal bed → infection or other pathology
Fourth: If diagnostic uncertainty exists
- Obtain fungal culture and microscopy for suspected infection 1
- Biopsy for any concern of melanoma - this takes priority over all other considerations
Critical Pitfall to Avoid
Do not assume all dark toenail discoloration is benign hematoma, especially without clear trauma history. The failure to diagnose subungual melanoma early has devastating mortality implications. When in doubt, biopsy or refer to dermatology 1.