Updated: 2/1/2019

Mycobacterium leprae

Review Topic
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  • A 35-year-old man presents to the dermatology clinic for a rash. He reports that these spots have been on his skin for about 2 months now since he returned from a work-stay program in South America. There he interacted with animals and occasionally tried exotic foods, such as the armadillo. On physical exam, there are multiple well-circumscribed erythematous plaques with raised borders and central hypopigmentation. There is loss of sensation over the plaques. He is started on a long course of antibiotics.
  • Classification
    • Mycobacterium leprae
      • a non-motile, acid-fast bacillus
      • prefers cool temperatures
    • transmission
      • respiratory via nasal mucosa
      • via armadillo reservoirs
  • Epidemiology
    • incidence
      • more common in Southeast Asia and South America
    • location
      • affects skin and peripheral nerves
    • risk factors
      • travel to endemic countries
      • contact with others with leprosy
      • contact with or consumption of reservoirs such as armadillos
  • Pathogenesis
    • the bacteria grows in cool regions, such as the skin and peripheral nerves
    • infects macrophages, Schwann cells, and keratinocytes
    • lepromatous Hansen disease
      • weak cell-mediated immunity
      • humoral Th2-type immune response
      • high burden of bacteria in lesions
    • tuberculoid Hansen disease
      • strong cell-mediated immunity
      • Th1-type immune response
      • low burden of bacteria in lesions
  • Associated conditions
    • lepromatous Hansen disease
    • tuberculoid Hansen disease
    • erythema nodosum
  • Prognosis
    • slow progression that may develop over months or years
    • may have intermittent acute leprosy reactions
    • lepromatous type is more severe
  • Symptoms
    • lepromatous Hansen disease
      • diffuse rash
    • tuberculoid Hansen disease
      • multiple discrete lesions
  • Physical exam
    • patients often present with overlapping findings
    • peripheral neuropathy
      • foot drop
      • facial nerve palsy
      • contractures or hand or feet
      • loss of sensation
    • lepromatous Hansen disease
      • leonine facies (lion-like)
        • thickened foreheard, ears, eyebrows, and cheeks
      • diffuse plaques and nodular skin lesions symmetrically distributed
        • may be erythematous or hypopigmented without sharp borders
    • tuberculoid Hansen disease
      • multiple discrete erythematous plaques with central hypopigmentation and raised discrete borders
        • plaques often have loss of sensation
        • hairless
        • dry with some scale
  • Labs
    • tissue polymerase chain reaction (PCR)
    • may test as falsely positive on VDRL testing
  • Biopsy or slit-skin smear
    • acid-fast bacilli
    • granulomas
  • Making the diagnosis
    • based on clinical presentation and tissue diagnosis
  • Morphea
    • distinguishing factor
      • also presents with thickened skin but usually does not involve peripheral nerve damage
  • Vitiligo
    • distinguishing factor
      • also presents with hypopigmentation but without peripheral nerve damage or raised borders
  • Medical 
    • dapsone and rifampin
      • indication
        • tuberculoid and lepromatous types
    • clofazimine
      • indication
        • added therapy for lepromatous types
  • Permanent nerve impairment
  • Deformities

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Questions (4)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2

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(M1.MC.15.75) A 29-year-old man who recently emigrated from South America presents complaining of a patch of numbness on his skin. He reports that the area has appeared paler than the surrounding skin for a long time. He also has had several cuts and burns near the area, but has no recollection of when the injuries took place and did not feel any pain at the time. On physical exam, you palpate an enlarged ulnar nerve at the elbow. Relevant additional findings from your physical exam are shown in Figure A. You order a biopsy from the edge of the lesion (Figure B). Which of the following most likely caused his disease? Review Topic | Tested Concept

QID: 106735





Mycobacterial infection




Sporothrix schenckii




Contact dermatitis




Poxvirus infection



L 2 D

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