Archive for the ‘Diseases’ Category

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The Story of Malaria

Wednesday, June 10th, 2009

Malaria is a mosquito borne illness caused by the female anopheles mosquito. Each year 350-500 million cases of malaria occur worldwide, and over one million people die, most of them young children in Africa south of the Sahara (CDC).

The British Medical Journal has uploaded a 10 minute YouTube video (Death by Mosquito) on the origins of malaria as we understand it now. Prior to the paper published in the BMJ in 1900, malaria was thought to be an airborne infection (mal = foul).

In 1900 Patrick Manson wrote a seminal paper in the BMJ Experimental Proof of the Mosquitomalaria Theory he worked closely with Ronald Ross, who went on to win the Nobel Prize for medicine for his work on malaria.


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Thromboangiitis Obliterans

Monday, March 23rd, 2009

(Double click any word for definition)

Also known as Buerger’s Disease (not to be confused with Berger’s disease which is IgA nephropathy)

Small – medium sized blood vessels involved

Strongly linked to tobacco use – smoking (both active and passive) and nicotine patches

Unclear etiology

More common in men than women (3:1)

Typical age group 20 – 45 years


Clinical Features

Diagnosis of exclusion

Typically age is < 45 years

Current or history of tobacco use

Presence of distal extremity ischemia (indicated by claudication, pain at rest, ischemic ulcers, or gangrene) documented by noninvasive vascular testing

Consistent arteriographic findings in the clinically involved and noninvolved limbs

Patients may describe a Raynaud type phenomenon in hands or fingers

Superficial migratory thrombophlebitis may occur

Parasthesias of hands & feet with impaired distal pulses (proximal pulses are generally normal)

Allen test may be positive


Workup

Labs are typically geared towards ruling out other causes

Angiography – may be required in all limbs as TAO may be clinically silent

Typical angiography features include:

  • Nonatherosclerotic
  • Segmental
  • Involvement of small- and medium-sized vessels
  • Formation of distinctive small-vessel collaterals around areas of occlusion known as “corkscrew collaterals”

Echo should always be performed to rule out embolic source


Treatment

Absolute discontinuation of tobacco use

Symptomatic management

  • Protective footwear
  • Avoid injuries and cold
  • Avoid medications which cause vasoconstriction

Surgical options:

  • Due to involvement of small vessels bypass grafting has limited value
  • Omental transfer
  • Sympathectomy
  • Spinal cord stimulator implantation

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Neurosarcoidosis

Sunday, March 15th, 2009

(Double click any word for definition)

The frequency of neurologic involvement is generally 5% of all cases of sarcoidosis

About two thirds of patients with neurosarcoidosis have a self-limited monophasic illness, the rest have a chronic remitting relapsing course

Occurs in adults aged 25-50 years

Neurosarcoidosis generally occurs within 2 years of onset of sarcoidosis

If diagnosis of sarcoidosis is known then symptoms may not pose diagnostic challenge (however other differential should be kept in mind esp. Infections)


Clinical Features

Any cranial nerve may be involved

Facial nerve most commonly involved – (Heerfordt syndrome – fever, uveitis, facial nerve palsy)

Peripheral nerve involvement – Mononeuropathy, mononeuritis multiplex, polyneuropathy

Central nervous system involvement may affect the hypothalamus/pituitary gland, cerebral cortex, cerebellum, and rarely spinal cord

Space-occupying lesion of brain (necrotizing sarcoidosis may manifest as agranulomatous mass lesion)

Hypopituitarism (and other endocrine manifestations)

Optic neuritis leading to optic atrophy (and other forms of eye involvement)

Meningitis, especially basal brain involvement

Cerebral infarct or transient ischemic attack due to vasculitis

Spinal cord lesions are rare (Intramedullary lesions resemble demyelinating disease)

Brain stem (sarcoid brainstem encephalitis) and cerebellar involvement (rare)

Seizures may be the first manifestation of neurosarcoidosis

Look for other signs of “regular” sarcoidosis


Workup

CSF may be normal 30%. When abnormal CSF may have nonspecific pattern with high protein level (>0.5 g/L), high leukocyte count (>5 cells/µL), usually lymphocytosis

ACE, lysozyme, and beta2-microglobulin can be elevated in the CSF

Imaging (esp MRI & CT brain) may localize lesions and give other clues

Biopsy of involved tissue to look for non-caseating granulomas


Treatment

Immunosuppressive therapy steroids, azathioprine, cyclosporine, cyclophosphamide, infliximab and methotrexate

Low dose cranial irradiation

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Methemoglobinemia

Sunday, March 8th, 2009

(Double click on any word for definition)

Hemoglobin contains 4 heme groups and each heme group contains Fe2+

When Fe2+ gets oxidized to Fe3+ it is called MetHb

MetHb not only reduces the oxygen binding capacity of Hb but interferes with oxygen unloading to the tissues thereby shifting the oxygen dissociation curve to the left

Under physiologic conditions MetHb is continuously produced due to the oxidizing effect of oxygen but is reduced back to Hb by cytochrome b5 reductase (NADPH MetHb reductase)

Normal levels of MetHb in humans < 2%

5 g/dl of deoxyHb produces cyanosis

MetHb produces cyanosis at 1.5 g/dl

Most commonly caused by drugs:

Benzocaine

Dapsone

Primaquine

Lidocaine

Nitrates

Sulfonamides

Prilocaine

Nitroprusside

Phenazopyridine

Pulse oximetry & Co-oximetry

Regular pulse oximeter measures UV absorption only 2 wavelengths for oxyHb (940nm) and deoxyHb (660)

Co-oximeter measures light absorption of blood at multiple UV wavelengths

They can measure the percentages of oxyHb, deoxyHb, carboxyHb and MetHb

Require a blood sample – cannot be used for continuous monitoring

Pulse oximeter is unreliable for measuring MetHb because methemoglobin is detected by both the oxyHb (940 nm) and deoxyHb (660 nm) sensors of the oximeters

At low levels (20%), methemoglobin is detected primarily by the deoxyHb sensor,and a pulse oximeter may show a falsely low oxygen saturation

At high methemoglobin levels (70%), detection by the oxyhemoglobin sensor pre- dominates, and a pulse oximeter may show a falsely high reading

Methylene blue, the antidote for MetHb, is also detected by the pulse oximeter’s deoxyHb sensor, which leads to the potential for falsely low post-treatment oxygen saturation readings

Clinical findings

Cyanosis unresponsive to oxygen

Cyanosis in the presence of normal (calculated) oxygen saturation

Saturation gap = Calculated sat – pulse oxymetry

Suspect presence of abnormal Hb if the saturation gap > 5% (+ or -)

Saturation gap is not proportional to MetHb level

Treatment

Symptomatic and those with MetHb > 20% should receive methylene blue

Methylene blue acts as a cofactor for NADPH MetHb reductase thereby converting Fe3+ to Fe2+ in Hb

Methylene blue is not effective in patients with G6PD deficiency as they have very low levels of NADPH – will cause hemolysis

Side effects of methylene blue includes bluish skin which may complicate assessment of cyanosis

Methylene blue also causes MetHb (in higher doses) !!!!!

If not responding to methylene blue – ? sulfHb, ongoing toxicity esp if toxin is ingested or G6PD deficiency – you may also have to consider an alternative diagnosis !!!

Rarely hyperbaric oxygen and/or exchange transfusion may be done

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Congenital Long QT Syndromes

Monday, March 2nd, 2009

A brief review of congenital long QT syndromes. I have limited this review to cover the main clinical concepts and have therefore left out the molecular physiology and genetics of these complex group of disorders.

Congenital Long QT Syndrome

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