CPD: Lyme Disease

[liveonearth]

ETIO:
causative organism: Borrelia burdorferi, a spirochete
vector: deer tick genus: Ixodes, species: dammini or pacificus

how to remove a tick: cover with vaseline and leave for a while, then pull out tick

EPIDEMIOLOGY:
most prevalent in New England, Great Lakes region esp Minn and Wisc, California, Oregon, Deep south
cases in 43 states
also in Europe, Asia, Australia

and by county in the US:

incidence is increasing in Minnesota

occurs most in summer


INITIAL SX:
onset 3-32 days after tick bite, 7 days median
initial: fever, malaise, fatigue, headache, stiff neck, myalgia
arthralgia may precede or accompany rash
sxs intermittent and changing but fatigue/malaise may linger for weeks

THE RASH
bull's eye rash called erythema chronicum migrans (ECM)
begins as red macule/papule
rash usu appears on thigh, buttock or axilla (75%)
could be anywhere ticks can bite, esp scalp where rash might be missed
(ticks love the hair line and behind the ears)

rash not always present, or not always noticed
rash is semi-circular and red, may have concentric circles on outer border
central clearing or induration, necrosis or vesiculation
days later secondary lesions may appear without the central clearing, smaller

all lesions non-tender and hot, perhaps burning discomfort
fade in about a month
may recur and vanish
urticaria common

WEEKS LATER:
NEURO
neurological signs in 15% of cases
usually resolve completely
lymphocytic meningitis (CSF has up to 100 lymphocytes/ml)
encephalitis with cranial nerve involvement: chorea, ataxia, craniel neuritis, peripheral neuropathy
CARDIAC
8% of pts have sx within weeks of ECM
AV block, pericarditis, cardiomegaly
MYALGIA/ARTHRALGIA
in about 50% of pts within weeks to months to 2 years of ECM
usu a sudden swelling, may be painful, in a single large joint
knee most common, then wrist, ankle, TMJ, shoulder, hip, elbow
recurs for years
about 10% of pts develop chronic knee involvement

LABS
usu AB detection tests
no national standards for best antigen
labs differ wildly
many false positives and negatives
a negative does not rule out Lyme
CDC recommends screening in two steps:
1) ANTIBODY TITER, either total or separate IgM and IgG
2) confirm positives with WESTERN BLOT
if IgM was positive then 2 of 3 bands are positive: 23, 39, 41 kd
if IgG then any 5 bands is a positive: 18, 21, 28, 30, 39, 41, 45, 58, 66, 93 kDa
some recommend other bands or skipping AB titers
antibodies only confirm exposure, not disease
CDC is only org offering recommendations
pts may continue to produce IgM indefinitely, and IgM and IgG may both be present
even after successful treatment IgG and IgM may persist in CSF
don't do the antibody titer if the rash is still present: the antibodies develop later
untxd pts with extracutaneous involvement almost always have positive titers
SYNOVIAL FLUID usu inflammatory (500-98,000 cells/microliter)
in older pts examine synovial fluid for crystals (rule out gout & pseudogout)
SPINAL FLUID needed if neuro sx but dx uncertain, measure IgM and IgG AB's to B. burdorferi and calculate index of CSF to serum antibody (immunoglobulin to albumin ratio)

DDX
in kids: JRA
in adults: Reiters syndrome, atypical RA (no morning stiffness, subQ nodules, RF or ANA)
hepatitis (10% of Lyme pts have RUQ pain, N/V, anorexia)
infectious arthritis
MS with neuro signs
acute rheumatic fever (post strep)
herpes zoster