Differentials
Psoriasis
SIGNS / SYMPTOMS
Presents with widespread scaly plaques of the skin, especially on the extensor aspects of joints. May be involvement of the nails and arthritis.
There is no neural involvement, and skin nodules are not found.
INVESTIGATIONS
Diagnosis is usually based on the appearance of the skin. There are no special blood tests or diagnostic procedures but a skin biopsy may be needed to rule out other disorders and to confirm the diagnosis.
Skin biopsy histology shows acanthosis of the epithelium, absence of granulomas, but focal accumulation of lymphocytes and neutrophils. No acid-fast-bacilli (AFB) are present in the biopsy.
Eczema
SIGNS / SYMPTOMS
Features widespread dryness of the skin and recurring skin rashes with erythema or pruritus.
Areas of temporary skin discoloration may appear.
Likely to be found on the flexor aspect of joints. May be a history of allergy. There is no neural involvement, and skin nodules are not found.
INVESTIGATIONS
Skin biopsy and histopathology show spongiosis, but no granulomas.
Skin testing (patch testing) may be diagnostic in allergic eczema, and CBC may show peripheral eosinophilia. No acid-fast bacilli (AFB) are present in the biopsy.
Tinea corporis
SIGNS / SYMPTOMS
Annular lesions with active and scaly border. There is no neural involvement, and skin nodules are not found.
INVESTIGATIONS
Scraping and KOH are positive. No acid-fast bacilli (AFB) are present in the biopsy.
Scars/keloids
SIGNS / SYMPTOMS
Burns and other injuries may leave behind anesthetic scars. There is a history of trauma or burn. There is no neural involvement, and skin nodules are not found.
INVESTIGATIONS
Skin biopsy and histopathology show an increase in collagen within the dermis without inflammation or granuloma formation. No acid-fast bacilli (AFB) are present.
Syphilis
SIGNS / SYMPTOMS
Syphilitic skin lesions may resemble the maculae of leprosy, but the absence of sensory changes and reaction to treatment are sufficiently distinctive.
INVESTIGATIONS
The infectious organism is Treponema pallidum. Skin biopsy and histopathology may show inflammatory changes, depending on the stage at presentation. Secondary syphilis may be associated with granuloma formation, but no acid-fast bacilli (AFB) are present on special stains.
The venereal disease research lab (VDRL) reaction alone cannot always be depended on in differential diagnosis, as false-positive reactions are not uncommon in borderline lepromatous and lepromatous leprosy, in which case confirmatory tests such as FTA-ABS are necessary.
Examination of skin scrapings or skin biopsy with dark field microscopy may visualize the spirochetes.
Systemic lupus erythematosus
SIGNS / SYMPTOMS
Skin lesions can be annular with raised border and central clearing similar to borderline leprosy.
INVESTIGATIONS
Positive antinuclear antibodies (ANA). Patients with leprosy often have false positive ANA, in which case specific antibodies to dsDNA may differentiate.
Mycosis fungoides
SIGNS / SYMPTOMS
Early lesions might be mistaken for nodular leprosy. Late-stage disease may have systemic involvement.
INVESTIGATIONS
Skin biopsy and histopathology are diagnostic, with infiltrates of atypical lymphocytes and clonality on T-cell gene re-arrangement studies.
Lupus vulgaris
SIGNS / SYMPTOMS
Highly likely to be mistaken for leprosy lesions, and in both diseases acid-fast bacilli are difficult to demonstrate. Lupus produces painful, ulcerating skin lesions around the mouth, eyes, nose, and ears. There is a greater tendency to scar formation, and there are no sensory changes.
INVESTIGATIONS
Skin biopsy will show granulomatous inflammation and, occasionally, caseous necrosis with Mycobacterium tuberculosis acid-fast bacilli (AFB) on special stains. Distinction from leprosy is difficult, but in cutaneous tuberculosis, M tuberculosis can be grown in culture or demonstrated with polymerase chain reaction.
Cutaneous leishmaniasis
SIGNS / SYMPTOMS
Cutaneous leishmaniasis may be mistaken for leprosy. Papular lesions become ulcerated. Anergic leishmaniasis can resemble lepromatous leprosy.
INVESTIGATIONS
Skin scraping, and histopathology. Leishmania can be grown in culture (NNN media) or demonstrated by polymerase chain reaction.
Use of this content is subject to our disclaimer