AMBULATORY MEDICINE
54
■
Empiric therapy is often indicated in the absence of a suspected organic
etiology. Oral phosphodiesterase inhibitors (sildenafil, vardenafil,
tadalafil) are first-line therapy but are contraindicated with nitrates or ac-
tive cardiac disease (can cause hypotension and sudden death).
■
Psychosexual counseling is first-line therapy for psychogenic ED.
■
Second-line therapies include intraurethral alprostadil suppositories, vac-
uum constrictive pumps, and penile prostheses.
Prostatitis
The differential includes acute bacterial prostatitis, chronic bacterial prostati-
tis, nonbacterial prostatitis, and prostatodynia. See Table 2.15 for key features
of each.
SYMPTOMS/EXAM
Presents with irritative voiding symptoms and perineal or suprapubic pain.
Acute bacterial prostatitis is notable for the presence of fever and an exqui-
sitely tender prostate.
TREATMENT
Table 2.15 outlines the treatment of prostatitis and prostatodynia.
Genital Lesions
Table 2.16 outlines the differential diagnosis and treatment of STIs that pre-
sent as genital lesions. Figures 2.23 through 2.26 illustrate genital HSV le-
Rapid onset of ED suggests
psychogenic causes or
medication side effects. More
gradual onset is associated
with medical conditions. Low

The spectrum of pathology ranges from subacromial bursitis and rotator cuff
tendinitis to partial or full rotator cuff tear. Due to excessive overhead motion
(e.g., baseball players).
SYMPTOMS
Presents with nonspecific pain in the shoulder with occasional radiation down
the lateral arm that worsens at night or with overhead movement. Motor
weakness with abduction is seen in the presence of a tear.
TABLE 2.15. Treatment of Prostatitis and Prostatodynia
ACUTE BACTERIAL CHRONIC BACTERIAL NONBACTERIAL
PROSTATITIS PROSTATITIS PROSTATITIS PROSTATODYNIA
Fever +− −−
UA +− −−
Expressed Contraindicated. ++−
prostatic
secretions
Bacterial culture ++ −−
Prostate exam Very tender. Normal, boggy, or Normal, boggy, or Usually normal.
indurated. indurated.
Etiology Gram-
ᮎ rods (E. coli); Gram-ᮎ rods; less Unknown; perhaps Varies; includes voiding
less commonly gram-
ᮍ commonly enterococcus. Ureaplasma, dysfunction and pelvic
organisms (enterococcus). Mycoplasma, Chlamydia. floor musculature
dysfunction.
Treatment IV ampicillin and TMP-SMX; Erythromycin × 3–6 α-blocking drugs (e.g.,
aminoglycosides until fluoroquinolones × weeks if response at two terazosin) for bladder
organism sensitivities 6–12 weeks. weeks. neck and urethral
are obtained; then spasms;
switch to benzodiazepine and
fluoroquinolones × 4–6 biofeedback for pelvic

smear with ᮍ intranuclear lesion turns tissue white 1° lesion is first
inclusions and with papillae. seen.
multinucleated giant cells. Immunofluorescence or
darkfield microscopy of
fluid with treponemes.
Treatment Acute episodes: Acyclovir Trichloroacetic acid; Benzathine penicillin Azithromycin 1 g PO × 1
400 mg TID, famciclovir podophyllin G IM × 1; in penicillin- or ceftriaxone 250 mg
250 mg TID, valacyclovir (contraindicated in allergic patients, IM × 1.
1000 mg BID × 10 days pregnancy); imiquimod. doxycycline or tetracycline
(first episode) or × 5 PO × 2 weeks.
days (recurrence).
Suppression: Acyclovir
400 mg BID or
famciclovir 250 mg BID
or valacyclovir 500 mg
BID or 1 g QD.
AMBULATORY MEDICINE
57
E
XAM
■
Exam reveals pain with abduction between 60 and 120 degrees. Tears lead
to weakness on abduction (“drop arm test”).
■
Pain elicited by 60–120 degrees of passive abduction (impingement sign)
suggests impingement or trapping of an inflamed rotator cuff on the over-
lying acromion.
DIFFERENTIAL
■
Bicipital tendinitis: Due to repetitive overhead motion (e.g., throwing,

AMBULATORY MEDICINE
58
■
Referred pain: May be derived from a pulmonary process (e.g., pul-
monary embolism, pleural effusion), a subdiaphragmatic process, cervical
spine disease, or brachial plexopathy.
■
Adhesive capsulitis (frozen shoulder): Presents with progressive loss of
range of motion (ROM), usually more from stiffness than from pain. Can
follow rotator cuff tendinitis; more common in diabetics and older pa-
tients.
DIAGNOSIS
■
Diagnosis is made by the history and exam.
■
An MRI can be obtained if a complete tear is suspected or if no improve-
ment is seen despite conservative therapy and the patient is a surgical can-
didate.
TREATMENT
■
↓ exacerbating activities; NSAIDs.
■
Steroid injection is a common treatment but is no more effective than
NSAID therapy.
■
ROM exercises and rotator cuff strengthening can be initiated once acute
pain has resolved.
■
Refer to orthopedics for possible surgery if there is a complete tear or if no
improvement is seen with conservative therapy after several months.

post-trauma suggests a
ligamentous tear (with
hemarthrosis). Swelling
occurring hours to days after
trauma suggests meniscal
injury.
The thin female teenager who
is an “exercise nut” is
particularly prone to stress
fractures.
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59
Lower Back Pain (LBP)
Extremely common, with up to 80% of the population affected at some time.
Three-quarters of LBP patients improve within one month. Most have self-
limited, nonspecific mechanical causes of LBP.
EXAM
■
A 1° goal of initial evaluation is to rule out serious conditions as indicated
by neurologic or systemic findings (see below).
■
A straight-leg raise test is ᮍ and indicates nerve root irritation if passively
straightening the leg in the supine or seated position causes radicular pain
at less than a 60-degree angle. Has poor specificity (40%) but excellent
sensitivity (80%) for lumbar disk herniation.
TABLE 2.17. Common Knee Injuries
ILIOTIBIAL PATELLOFEMORAL MEDIAL MENISCUS
BAND SYNDROME ANSERINE BURSITIS PAIN SYNDROME TEAR ACL TEAR
Those Runners; Runners, obese or Runners/ Twisting of the knee Twisting trauma,
affected/ deconditioned deconditioned deconditioned while the foot is often in noncontact

diagnosis of cancer represents
metastasis until proven
otherwise. Spinal cord
compression is a
neurosurgical emergency.
AMBULATORY MEDICINE
60
TABLE 2.18. Common Causes of Foot and Ankle Pain
CAUSE SEEN IN/ETIOLOGY SYMPTOMS DIAGNOSIS TREATMENT
Plantar Obese patients, Plantar pain, especially Tenderness over insertion ↓ prolonged standing;
fasciitis prolonged standing, with first steps in of the plantar fascia at arch supports; NSAIDs;
runners. morning. the medial heel. Bone stretches. In 80% of
spurs on x-ray are cases, symptoms
neither sensitive nor resolve within one year.
specific for plantar
fasciitis.
Stress fracture Runners, especially Foot pain that worsens X-ray may miss early Hard-soled shoe or
women. with weight bearing. fractures. Obtain bone walking cast for 3–4
scan or MRI in the weeks. Avoid
presence of high exacerbating activities
suspicion and when x-ray until fully healed.
is ᮎ.
Metatarsalgia Seen in those with Pain in the area of the Clinical diagnosis; Avoid offending shoes;
prolonged pressure on metatarsal heads (one exclude other etiologies. NSAIDs.
the anterior feet, or multiple).
especially from high
heels.
Morton’s Entrapment of the Forefoot pain and Usually a clinical diagnosis Broad-toed shoes,
neuroma interdigital nerve. Affects paresthesias radiating (tenderness in affected orthotics, corticosteroid
women more than men. to toes; the third web web space); MRI can injections. Surgery should

Compression fracture: Age > 50, significant trauma, a history of osteo-
porosis, corticosteroid use.
■
Infection (epidural abscess, diskitis, osteomyelitis, or endocarditis):
Fever, recent skin or urinary infection, immunosuppression, IV drug
use.
■
Cauda equina syndrome: Bilateral leg weakness, bowel or bladder in-
continence, saddle anesthesia.
■
Less urgent causes of back pain include herniated disk; spinal stenosis;
sciatica; musculoskeletal strain; and referred pain from a kidney stone, an
intra-abdominal process, or herpes zoster. Table 2.20 outlines the distin-
guishing features of herniated disk and spinal stenosis.
DIAGNOSIS
■
The history and clinical exam are helpful in identifying the cause.
■
A plain x-ray is indicated only if fracture, osteomyelitis, or cancer is being
considered. Plain films are insensitive for metastasis, infection, and disk
disease.
■
MRI (or CT) is indicated urgently in cases of suspected cauda equina syn-
drome, cancer, or infection. For patients with suspected disk disease, imag-
ing is not indicated unless symptoms persist for > 6 weeks or significant
neurologic findings are present, particularly if surgery is being considered.
■
The specificity of MRI is low, and care should be taken to intervene only
when symptoms and physical findings can clearly be attributed to the ab-
normalities found on imaging.

Skin (herpes zoster),
Strain, Scoliosis, and
lordosis
Slipped disk/
Spondylolisthesis
AMBULATORY MEDICINE
TREATMENT
■
For mechanical causes of acute LBP, conservative therapy with NSAIDs
and muscle relaxants, education, and early return to ordinary activity are
indicated in the absence of major neurologic deficits or other alarm symp-
toms, as most cases of LBP resolve within 1–3 months. Bed rest is ineffec-
tive.
■
Massage and manipulation by a chiropractor or physical therapist are safe
and effective for benign, mechanical causes of LBP.
■
Spinal stenosis can be treated with exercises to ↓ lumbar lordosis. Epidural
corticosteroid injections provide some relief. Decompressive laminectomy
may provide at least short-term symptom improvement for a majority of
patients. Surgery for lumbar disk herniation is reserved for refractory radic-
ular symptoms (duration > 6 weeks) or severe motor deficits.
FIGURE 2.27.
Ottawa Ankle Rules for x-rays in ankle/foot trauma.
(Reproduced, with permission, from Tintinalli JE et al. Tintinalli’s Emergency Medicine: A
Comprehensive Study Guide, 6th ed. New York: McGraw-Hill, 2004.)
TABLE 2.19. Nerve Root Syndromes (Sciatica)
NERVE ROOT STRENGTH SENSORY REFLEXES
S1 Ankle plantar flexion (toe walking). Lateral foot. Achilles.
L5 Great toe dorsiflexion. Medial forefoot. None.

DIAGNOSIS
■
BP should be checked at least every two years starting at age 18.
■
Unless acute end-organ damage is present or BP is above 220/115, the di-
agnosis of hypertension requires multiple BP readings above 140/90 on at
least two different occasions.
■
The Joint National Committee on Prevention, Detection, Evaluation, and
Treatment of High Blood Pressure (JNC 7) identifies three goals of evalua-
tion: (1) assess lifestyle and other cardiovascular risk factors or other dis-
ease that will affect management (diabetes, hyperlipidemia, smoking); (2)
identify 2° causes of hypertension; and (3) assess for the presence of target-
organ damage and cardiovascular disease (heart, brain, kidney, peripheral
vascular disease, retinopathy).
■
Identifiable causes of hypertension include the following:
■
Sleep apnea
■
Drug-induced hypertension (e.g., NSAIDs, OCPs, cyclosporine, de-
congestants, cocaine)
■
Chronic kidney disease (most common)
■
1° aldosteronism
TABLE 2.20. Herniated Disk vs. Spinal Stenosis
HERNIATED DISK SPINAL STENOSIS
Etiology Degeneration of ligaments leads to disk prolapse, Narrowing of the spinal canal from osteophytes at
leading in turn to compression or inflammation of facet joints, bulging disks, or a hypertrophied

TREATMENT
■
The goal of BP management is < 140/90, or < 130/80 in patients with dia-
betes, renal disease, or cardiovascular disease.
■
All patients with prehypertension and stages 1 and 2 hypertension should
be counseled about lifestyle modification (see Table 2.22). If a brief trial of
nonpharmacologic therapy fails, medications should be added for those
with stage 1 or 2 hypertension (see Table 2.23).
■
Other modifiable cardiovascular risk factors (diabetes, hyperlipidemia,
smoking) should be screened for and treated in hypertensive individuals.
TABLE 2.21. Blood Pressure Classification
BP CATEGORY SYSTOLIC BP (mmHg) DIASTOLIC BP (mmHg)
Normal < 120 and < 80
Prehypertension 120–139 or 80–89
Stage 1 HTN 140–159 or 90–99
Stage 2 HTN ≥ 160 or ≥ 100
TABLE 2.22. Lifestyle Modifications for Hypertension
MEASURE COMMENTS
Sodium restriction No added salt or low-sodium diet.
DASH diet (Dietary Approaches to Stop A diet rich in fruits, vegetables, and low-fat
Hypertension) dairy products with ↓ saturated and
unsaturated fat.
Weight reduction If over the ideal BMI.
Aerobic physical activity
Limitation of alcohol consumption Limit to < 2 drinks per day for men and < 1
drink per day for women.
For most hypertensive
patients, thiazide diuretics are

studied in combination with either bupropion or nicotine replacement.
COMMON SYMPTOMS
Vertigo
An illusion of motion (a sensation that one’s “head is spinning” or that the
“room is whirling”) can originate in the peripheral (labyrinth/inner ear) or
central vestibular system. Other forms of dizziness include the following:
■
Presyncope: A feeling of impending loss of consciousness (“I’m going to
faint”). Usually due to postural changes rather than to arrhythmia or struc-
tural heart disease. See the Cardiology chapter for further details.
■
Disequilibrium: Unsteadiness with standing or walking (patients com-
plain that “my balance is off” or that “I feel as if I’m going to fall”). Com-
mon in older patients; often multifactorial.
■
Lightheadedness: Anxiety (“I’m just dizzy”).
SYMPTOMS
■
Presents with a sensation of exaggerated motion when there is little or no
motion.
■
Peripheral vertigo is often accompanied by nausea and vomiting; central
vertigo often occurs in conjunction with other posterior circulation find-
ings.
■
Ipsilateral facial numbness or weakness or limb ataxia suggests a lesion of
the cerebellopontine angle.
EXAM
■
Orthostatics.

Side effects Hypokalemia, ED, Bronchospasm, Cough (10%), No cough. Less Conduction defects
↑ insulin resistance, bradycardia/AV hyperkalemia, renal hyperkalemia, renal (nondihydropy-
hyperuricemia, node blockade, failure, angioedema. failure, angioedema. ridines); lower
↑ TG. Metabolic depression, fatigue, extremity edema
side effects are ED, ↑ insulin (dihydropyridines).
more prominent at resistance.
doses of > 25
mg/day.
Indications as Used in most MI, high CAD risk. DM with micro- ACEI cough in Systolic
first-line drug patients as mono- albuminuria/ patients who would hypertension,
or combination proteinuria; MI with otherwise have advanced age,
therapy (stage 1 or systolic dysfunction indications for ACEI. CAD.
2 hypertension), or anterior infarct;
including isolated non-DM-related
systolic proteinuria.
hypertension in the
elderly.
Other Recurrent stroke CHF, CHF. CHF, DM, chronic Atrial arrhythmias
indications prevention. May tachyarrhythmias, renal failure. (nondihydropy-
mitigate migraine. ridines), isolated
osteoporosis. systolic
hypertension in
elderly
(dihydropyridines).
Contra- Gout. Bronchospasm; Pregnancy. Pregnancy. High-degree
indications high-degree (type II heart block.
second- or third-
degree) heart block.
AMBULATORY MEDICINE
DIAGNOSIS/TREATMENT

Signs/diagnosis MRI. MRI/CT, angiogram. Diagnosis of exclusion. MRI/CT.
Treatment Surgery. Stroke treatment. β-blockers, ergots. See the Neurology
chapter.
67
Peripheral vertigo is often
more severe than central
vertigo but should not have
any associated neurologic
symptoms.
AMBULATORY MEDICINE
68
mortality. It is idiopathic in up to one-third of cases. Other etiologies are as
follows:
■
Cancer and GI disorders (malabsorption, pancreatic insufficiency) and
psychiatric disorders (depression, anxiety, dementia, anorexia nervosa) ac-
count for up to two-thirds of cases.
■
Other causes include hyperthyroidism, DM, chronic diseases, and infec-
tions. Difficulty with food preparation or intake from any cause (social iso-
lation with inability to shop/cook, ill-fitting dentures, dysphagia) should al-
ways be considered.
DIAGNOSIS
■
The history and exam often provide clues. Document the actual amount
of weight lost.
■
The initial evaluation should include CBC, TSH, electrolytes, UA, CXR,
and age-appropriate cancer screening tests.
■

AMBULATORY MEDICINE
69
■
Appetite stimulants (megestrol acetate, dronabinol) are sometimes used in
the presence of low appetite.
Fatigue
A common symptom that is most often due to stress, sleep disturbance, viral
infection, or other illnesses. Causes include the following:
■
Thyroid abnormalities (hypo- and hyperthyroidism)
■
Infections (hepatitis, endocarditis)
■
COPD
■
CHF
■
Anemia
■
Sleep apnea
■
Restless leg syndrome (RLS)
■
Psychiatric disorders (depression, alcoholism)
■
Drugs (β-blockers, sedatives)
■
Autoimmune disorders
Chronic fatigue syndrome is defined as fatigue lasting at least six months that
is not alleviated by rest and that interferes with daily activities, in combination

giness, a “cobblestone” oropharynx, wheezes, a prolonged expiratory
phase, and rales.
■
Once benign, self-limited causes such as postviral cough have been ruled
out, a CXR should be obtained before prolonged courses of empiric ther-
apy are initiated.
■
If the CXR is normal, a trial of empiric therapy for the most likely cause is
appropriate (see below).
Causes of chronic
cough—
GASPS AND COUgh
GERD
Asthma
Smoking, chronic
bronchitis
Postinfection
Sinusitis, postnasal drip
ACEIs
Neoplasm
Diverticulum
CHF
Outer ear disease
Upper airway
obstruction
AMBULATORY MEDICINE
70
■
If empiric therapy fails, consider PFTs (+/− methacholine challenge) for
suspected asthma. Esophageal pH monitoring is definitive for GERD.

out other sleep disorders, such as sleep apnea.
TREATMENT
■
Treat the underlying disorder.
■
Sleep hygiene and relaxation techniques are effective treatments for
chronic insomnia.
■
Benzodiazepines and benzodiazepine receptor agonists (zolpidem, zale-
plon) are FDA approved for the treatment of short-term insomnia (7–10
days). Only eszopiclone is FDA approved for the chronic treatment of in-
somnia. Antidepressants such as trazodone and antihistamines are com-
monly used off-label for this indication despite a lack of evidence for their
safety or efficacy.
Chronic Lower Extremity Edema
The differential for chronic bilateral lower extremity edema includes the fol-
lowing (see also Table 2.28):
■
Venous insufficiency: Risk factors include obesity and a history of preg-
nancy. Varicose veins may be the only finding in the early stages. Edema,
skin changes, and ulcerations (medial ankle) are later findings.
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■
Lymphedema: Can be idiopathic (due to a congenital abnormality of the
lymphatic system) or 2° to lymphatic obstruction (e.g., from tumor, filaria-
sis, lymph node dissection, or radiation). The dorsum of the foot is com-
monly affected. Late changes include a nonpitting “peau d’orange” ap-
pearance.
■
Varicose veins: May occur with or without chronic venous insufficiency.

Filariasis: Lymph node obstruction by Wuchereria bancrofti and Brugia malayi.
Drugs: NSAIDs, glucocorticoids, estrogen.
↑ capillary permeability Hypothyroid myxedema, drugs (calcium channel blockers, hydralazine), vasculitis.
↓ oncotic pressure Nephrotic syndrome, protein-losing enteropathy, cirrhosis, malnutrition.
71
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72
The differential for unilateral lower extremity edema is as follows:
■
Venous insufficiency: Post–vein graft for CABG, prior DVT, leg injury.
■
Reflex sympathetic dystrophy: Hyperesthesia and hyperhidrosis that occur
a few weeks after trauma; trophic skin changes and pain out of proportion
to the exam (see the discussion of complex regional pain syndrome be-
low).
■
DVT: Usually acute edema.
■
Infection: Cellulitis or fasciitis.
■
Inflammation: Gout; ruptured Baker’s cyst (posterior knee).
DIAGNOSIS
■
The etiology can often be determined without diagnostic testing.
■
Depending on the history and physical exam, consider ordering an
echocardiogram, a UA for protein, liver enzymes, and abdominal/pelvic
imaging to rule out systemic causes of edema or venous obstruction.
■
Lower extremity ultrasound with Dopplers can rule out DVT and demon-

Swelling.
■
Disturbances of color and temperature.
■
Dystrophic changes of affected skin and nails.
■
Limited ROM.
■
The shoulder-hand variant presents with hand symptoms along with lim-
ited ROM at the ipsilateral shoulder. May occur after MI or neck/shoulder
injury.
DIAGNOSIS
■
Bone scan is sensitive and reveals ↑ uptake in the affected extremity.
■
Later in the course, radiographs reveal generalized osteopenia.
AMBULATORY MEDICINE
73
T
REATMENT/PREVENTION
■
Early mobilization after injury/surgery/MI reduces the chance of develop-
ing CRPS and improves the prognosis once it has occurred.
■
Physical therapy is the mainstay of treatment and should focus on optimiz-
ing function of the affected limb.
■
TCAs are first-line pharmacologic therapy, but other neuropathic pain
medications (e.g., gabapentin, topical lidocaine) may also be tried. Pred-
nisone (40 mg × 2 weeks, tapered over 2 weeks) is sometimes used in resis-

lifestyle modifications.
Nonmaleficence Do no harm to your patient. Physician advises against epidural steroid injection
for chronic back pain due to spinal stenosis
because it is unlikely to benefit patient.
Justice The equitable distribution of resources within a Organ transplantation.
population.
Autonomy The right of patients to make their own decisions Patient gives informed consent (or refusal) to
about their health care. surgery.
Fidelity Truthful disclosure to patients. Physician informs patient that pneumothorax
occurred during thoracentesis.
Exceptions to the requirement
for informed consent include
life-threatening emergencies
or circumstances in which
patients waive their right to
participate in the decision-
making process.
AMBULATORY MEDICINE
74
■
If a patient lacks capacity to make decisions, their advance directive or as-
signed surrogate guides decisions.
Confidentiality
■
HIPAA, the Health Insurance Portability and Accountability Act of 1996,
provides specific guidelines governing when and how the sharing of confi-
dential patient information is acceptable.
■
Exceptions to the rule of confidentiality:
■

tient who suffers cardiac arrest due to hypotension refractory to multi-
ple vasopressors).
■
An intervention that has already been tried and failed in the patient (e.g.,
if cancer worsened despite a complete course of chemotherapy, there
would be no obligation to provide another course of the same therapy).
■
Treatment with no physiologic basis (e.g., plasmapheresis for septic
shock).
■
Ethical “gray zones” in futility include withdrawing care because the
chance of success is small or because the patient’s best outcome would be
a low quality of life. Ethics consultations are often required to sort through
these complex situations.
Resource Allocation
■
Physicians should use health resources judiciously and appropriately (i.e.,
they should avoid unnecessary tests, medicines, procedures, and consults).
A diagnosis of dementia does
not necessarily imply that the
patient lacks capacity to make
decisions, as long as the
patient can satisfy the
requirements of decision-
making capacity.
AMBULATORY MEDICINE
75
■
A physician’s primary responsibility is to his/her patient, and larger re-
source allocation decisions should be made at the societal, policy level.

Proctitis: Screen for N. gonorrhoeae, C. trachomatis, HSV, and syphilis.
■
Offer HBV and HAV vaccines.
■
Anal Pap smear: In HIV-ᮍ MSM, this test has characteristics similar
to those of the cervical Pap.
■
In women who have sex with women, cervical cancer screening should
proceed according to standard guidelines (see the discussion of cancer
screening above) even if patients have never had heterosexual contact.
EVIDENCE-BASED MEDICINE
Major Study Types
Table 2.30 outlines the major types of studies seen in the medical literature.
Test Parameters
Test parameters measure the clinical usefulness of a test. These include the
following:
■
Sensitivity (Sn)—“PID” (Positive in Disease): The probability that a
given test will be
ᮍ in someone who has the disease in question.
■
Specificity of a test (Sp)—“NIH” (Negative in Health): The probability
that a given test will be
ᮎ in someone who does not have the disease in
question.
A highly Sensitive test, when
Negative, rules out the
disease (SnNout).
A highly Specific test, when
Positive, rules in the disease

determining exposure. in utero exposures. subject to more rigorous
study.
Cross- Identifies exposure and Checking for hypertension Often survey data. No ability to detect
sectional outcome at the same and concurrently temporal relationship
study time for each subject obtaining data on obesity between exposure and
within a specified in all persons seen in San outcome.
population. Francisco county clinics.
Systematic Summarizes the results Qualitative review of all Sets forth rigorous criteria Studies are often too
review of multiple individual trials of omega-3 fatty to determine which small or too
trials addressing the acids for the prevention studies will be included heterogeneous to apply
same (or similar) of cardiovascular disease. or excluded from the rigorous statistical
research questions. review. This helps limit methods to the summary
bias in the summary analysis. Qualitative
conclusions. summary conclusions are
substituted for numeric
data.
Meta-analysis A subset of systematic Cochrane review of all Provides an estimate of Uses a variety of
reviews. Quantitative randomized trials treatment effect, statistical methods.
compilation of data from comparing glucosamine including magnitude of Different meta-analyses
multiple small studies to with placebo or other effect, when individual of the same data can
generate a pooled result. treatments for patients studies are too small to produce different results.
with OA. derive robust conclusions. When component studies
are heterogeneous, it is
difficult to interpret/use a
pooled result.
76
AMBULATORY MEDICINE
77
■
Positive predictive value (PPV): The probability that a disease is actually

■
LR (ᮍ) = (sensitivity) / (1 − specificity).
■
LR (−) = (1 − sensitivity) / (specificity).
An illustrative example of how to calculate PPV, NPV, and LRs, and how they
depend upon disease prevalence, is outlined below.
■
For a given disease, the diagnostic test under consideration has the follow-
ing characteristics:
■
Sensitivity = 90%.
■
Specificity = 95%.
■
For this test, then, the likelihood ratios of ᮍ and ᮎ results are as follows:
■
LR (+) = 0.90 / (1 − 0.95) = 18.
■
LR (−) = (1 − 0.90) / 0.95 = 0.105.
■
Note that because the LRs are far from 1, this test appears to be useful
both for ruling disease in and for ruling it out. However, disease preva-
lence in the population has a crucial effect on test performance, as seen
below.
■
Suppose the disease prevalence in the population in question is 20%.
Given a total population of 1000 individuals, the 2 × 2 table of disease sta-
tus/test result can be constructed as shown in Table 2.32.
TABLE 2.31. Calculating PPV and NPV
DISEASE PRESENT DISEASE ABSENT