What is onychomatricoma?

Onychomatricoma: A Rare Benign Nail Matrix Tumor

Onychomatricoma is a rare benign fibroepithelial tumor originating from the nail matrix that is often misdiagnosed as onychomycosis due to similar clinical appearance. 1, 2

Clinical Characteristics

Onychomatricoma presents with distinctive features:

• Typical presentation:

  • Thickened nail plate with increased transverse curvature
  • Yellow discoloration (xanthonychia) of the affected nail
  • Longitudinal ridging or splitting of the nail plate
  • Splinter hemorrhages in the proximal portion of the nail
  • Multiple small cavities in the nail plate (described as "woodworm-like" holes)
  • Often affects a single nail 2, 3, 4

• Common locations:

  • First three fingers of the dominant hand
  • Big toe
  • More common in middle-aged women, but can occur in any age group (including children) 2, 5

Diagnostic Approach

Diagnosis requires a high index of suspicion and confirmation through:

1. Clinical examination:

   • Look for thickened nail with increased curvature
   • Observe for yellow discoloration and splinter hemorrhages
   • Check for woodworm-like cavities in the nail plate 3, 4

2. Imaging studies:

   • MRI or ultrasound may suggest the diagnosis
   • Can help determine extent of the lesion 2

3. Dermoscopy:

   • Shows parallel lesion edges and splinter hemorrhages
   • Helps differentiate from squamous cell carcinoma 2

4. Definitive diagnosis:

   • Requires biopsy and histopathological examination
   • Complete excision of the tumor is both diagnostic and therapeutic 1, 2

Histopathological Features

Onychomatricoma has distinctive histological characteristics:

• Proximally: Fibroepithelial tumor with fibrous stalk pierced by epithelial invaginations
• Distally: Tumor pierces the nail plate as glove-finger digitations
• Multiple empty channels ("worm holes") in the nail plate
• Epithelium shows matrical differentiation 2

Differential Diagnosis

Important conditions to differentiate from onychomatricoma include:

• Onychomycosis - most common misdiagnosis, requires mycological testing for confirmation 6, 7
• Fibrokeratoma
• Melanonychia
• Periungual fibroma
• Squamous cell carcinoma 2

Treatment

Complete surgical excision of the tumor is the treatment of choice and is generally curative. The procedure should include:

• Removal of the affected nail plate
• Complete excision of the tumor from the nail matrix
• Follow-up to monitor for recurrence 1, 2

Important Clinical Considerations

• Onychomatricoma is frequently misdiagnosed as onychomycosis, with approximately 15 out of 80 reported cases initially misdiagnosed 1
• Consider onychomatricoma in cases of suspected onychomycosis that fail to respond to antifungal treatment 1
• Nail trauma or fungal infection may play a causative role in the pathogenesis 2
• Onychomatricoma can coexist with onychomycosis in the same nail 5
• The clinical index of suspicion should increase when only a single dystrophic nail is involved 1

Prognosis

After complete surgical excision, the prognosis is excellent with low recurrence rates. Patients should be monitored for at least 12 months post-excision to ensure no recurrence 1.