Differential Diagnosis of Leprosy

Leprosy is a chronic infection caused by the acid-fast, rod-shaped bacillus Mycobacterium leprae.

It is a disease that primarily affects superficial tissues, especially the skin and peripheral nerves.

It is an airborne infection (like tuberculosis) which affects skin and nerves.

Leprosy often presents with hypopigmented or slightly erythematous patches on the skin with loss of sensation, and enlarged nerves.

Loss of sensation is tested with a whisk of cotton wool.

Unlucky patients, those who are diagnosed at later stages with nerve damage may show visible deformities such as facial palsy (an eye cannot close, lagophthalmos, and that side of the face sags)

There may be loss of sensation of hands or feet which show dry skin with or without ulcers. Sometimes fingers are bent or even lost, the grip is gone, the feet drop

• Paucibacillary (PB) leprosy or tuberculoid leprosy: These patients do not have bacilli in their skin smears and have 5 or fewer skin lesions. They are not infectious to others.
• Multibacillary (MB) leprosy or lepromatous leprosy: These patients have bacilli in their skin smear and more than 5 lesions which may be flat or raised patches, papules, or nodules. Untreated lepromatous leprosy patients discharge bacilli from their nose and are therefore infectious to others.

In an endemic area of leprosy, a practitioner confronted with a patient with an acute or chronic atypical rash that is not diagnostic and/or fails to respond to treatment would generally have leprosy in their differential diagnosis.

• Investigate for potential exposure to the infection from an endemic area.
• Assess the clinical characteristics of the rash:
  • Is it localized or disseminated?
  • Is it asymmetric or symmetric?
  • Is there diffuse infiltration of the skin?
• Look for evidence of any specific clinical manifestations, such as:
  • Neurologic or ocular changes
  • Acral edema
  • Testicular swelling or tenderness
  • Mastitis
  • Dactylitis
  • Synovitis
  • Arthritis
• Conduct diagnostic tests, including:
  • Scrapings of skin lesions and cooler sites of the skin (ears, chin, elbows, and knees) to check for the presence of acid-fast bacilli.
  • Biopsy of relevant sites to confirm the presence of the mycobacteria, often done using the Fite-Faraco stain.
• Sometimes, leprosy may present with neural symptoms alone.

How to Diagnose Leprosy

• Examine the patient's skin.
• Check for the presence of skin patches.
• Test the sensation in affected areas.
• Count the number of skin patches.
• Look for any signs of nerve damage.

Signs of Leprosy

• Pale or slightly reddish skin patch.
• Definite loss of sensation in the affected patch.
• Signs of nerve damage, including:
  • Definite loss of sensation in the hands or feet.
  • Weakness of muscles in the hands, feet, or face.
  • Visible deformities in the hands, feet, or face.

Skin patches that are:

• Normal in feeling.
• Present from birth.
• Itchy.
• White, black, dark red, or silver-colored.
• Display scaling.
• Appear and disappear periodically.
• Spread quickly.

Signs of damage to hands, feet, or face:

• Due to other reasons like injury, accidents, burns, or birth defects.
• Due to other diseases like arthritis.
• Due to other conditions causing paralysis.

Check for Loss of Sensation

1. Take a pointed soft object (feather, cotton wick).
2. Lightly touch alternately the patch and normal skin.
3. Ask the person to point to where they were touched.
4. Ask them to close their eyes and repeat the procedure.
5. In case of loss of sensation, the person will be able to point to where they were touched on the normal skin but not on the patch.

Non-granulomatous non-infectious conditions

• Hypopigmented lesions (e.g., vitiligo, acquired post-inflammatory hypopigmented lesions with or without scaling)
• Contact dermatitis
• Nummular eczema
• Psoriaform eruptions
• Drug eruptions
• Lichenoid dermatitis

Infectious mimickers

• Tinea corporis
• Pityriasis versicolor
• Granuloma annulare
• Morphea
• Scleroderma

Granulomatous diseases

• Sarcoidosis
• Cutaneous leishmaniasis
• Secondary syphilis, tertiary syphilis
• Lymphoproliferative disease
• Deep fungal infections - blastomycosis, histoplasmosis, mycetomas

Differentials of leonine facies

• Mycosis Fungoides
• Mastocytosis
• Amyloidosis
• Leishmaniasis
• Progressive nodular histiocytosis