SLIT SKIN SMEAR OF SLIT SKIN SMEAR OF M. LEPRAEM. LEPRAE

Dr. Abe MathewSkill Presentation

40 year old patient had come with C/O hypoanesthetic patches over the face and both the arms. O/E: decreased sensation over the patches, thickened ulnar nerve and common peroneal nerves.

TECHNIQUETECHNIQUE

� Skin and nasal secretions provide readily available specimens.

� All entirely relate to demonstration of AFB as M. Leprae cannot be cultured.

� Scrapings from skin lesions std. technique.� Estimate no. of M. Leprae in pts. lesions- BI

& proportion of viable bacteria – MI.

� Site cleared with cotton alcohol swab. Skin pinched to exert pressure to decrease bleed. Cut of 5mm long and 3mm depth made.

� Side of cut is scrapped several times – obtain little pulp tissue from below epidermis. Transfer to slide.

� Spread in circular motion by flat of blade to produce uniform and moderate thick smear over an area 5-7mm diameter.

� Previously untreated/ suspected relapse: smear from 6 sites- both ear lobes and 4 active skin sites.

� Treated patients(responded to therapy) and non lepromatous: from sites previously positive – both ear lobes and representative areas of skin.

FIXATION:� Smears are air dried. MC further fixed by heating. � Best – heat for 5 min. between 40-50 degrees.

ACID FAST STAINING:� Stain with carbol fuschin� Heat to cause steaming. Cool for 15 min.� Washed gently with tap water.� Destain with alcohol(70%) until colorless.� Wash with tap water.� Counterstain with methylene blue for 1 minute.

MEASUREMENT OF BI:� Measuring density of bacteria in lesion is based on

counting the AFB.� Most reliable and recommended one is based on

logarithmic scale.� Measurement carried out under oil immersion by

determining no. of AFB/ field after examining 25-100 fields on a logarithmic scale ranging from 0-6.

� Smears containing many RBC’s discarded.� All AFB counted whether stained uniformly or

irregular.

AVG. NO. OF AFB>1000/field100-1000/field10-100/field1-10/field1-10/10 fields1-10/100 fields0/100 fields

BI6+5+4+3+2+1+0+

BI= Scores of smears from a no. of different skin sites added together divided by the no. of sites.

� Mathematically incorrect since it is a compound of an arithmetic mean with a logarithmic component.

� Untreated patients with LL – BI fo range 6+ to 5+.� BT leprosy – 0-2+� TT leprosy – 0

MEASUREMENT OF MI:� Carbol fuschin stained M. Leprae show variable

morphology – stained regular/ irregularly.� Clinical observations showed proportion of

irregularly stained bacteria increased following treatment – so Writers and Rees introduced index based on morphology to measure (1)viability and to measure (2)patients response to treatment.

� MI is undertaken on same stained slit SS used to measure BI.

� Fields are picked at random. No. of irregularly and regularly stained bacteria counted on until atleast 100 organisms are available.

� Only individual bacteria, entire outline which are seen and which are not touching or superimposed counted.

� Bacteria showing uniform and bright staining down their length – regularly stained. Palely stained organisms –irregularly stained.

� Short organisms(<4 times their width) – irregularly stained.

� MI is given as proportion or % of regularly stained bacteria of total scored.

� Does it help?Guide for determining infectiousness of patientPatients response to treatmentIn treated patients +ve MI – shows relapse/ poor compliance/ drug resistance.

� Problems? – technically demanding/ very precise staining conditions/ skilled staff/ high quality microscopes

� REFERENCESControl of leprosy in CommunityPark and Park