Microcystin: the hepatotoxin that shut down Toledo’s water supply




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The Toxicology of Microcystins. Dawson RM. Toxicon 1998;36:953-962.


Just when you thought it was safe to go back to the faucet . . .

While I was on vacation, the big toxicology story involved contamination of the water supply to Toledo Ohio. As a result almost half a million people in the area were warned not to drink — or even shower with — water from Lake Erie.

The cause was a bloom of freshwater cyanobacteria, resulting from increased levels of phosphates and fertilizer. These cyanobacteria product microcystin, a heat-stable hepatotoxin. Microcystin can cause 3 clinical syndromes:

  1. Gastroenteritis (nausea, vomiting,diarrhea)
  2. Allergic and irritant reactions on local contact
  3. Liver damage

Microcystin interferes with the function of the hepatic cytoskeleton, causing necrosis and massive liver hemorrhage. Death is from hemorrhagic shock. Since the toxin is heat-stable, boiling water will just increase the concentration. Likewise, treating with chlorine may kill the organism and result in increased toxin release.

Hepatotoxicity requires that toxin be transported into the liver cell, a process that is blocked by the antibiotic rifampin. Administering rifampin prior to, or at the time of, microcystin exposure can be protective — at least in mice. It is not clear if this can provide any clinical benefit in human cases.

In 1996, 50 patients at a dialysis center in Brazil died of acute liver failure after exposure to water contaminated with microcystin.

A Chest Radiograph after Cardiac Surgery

aka Labs and Lytes 017

Author: Kathy Jao
Reviewer: Chris Nickson

You review a chest radiograph taken of an intubated patient who has been transferred to the ICU following cardiac surgery:

Jao CXR 1b

Q1. Describe and interpret the chest radiograph.

This supine AP CXR demonstrates a correctly sited endotracheal tube (ETT), a left internal jugular central venous catheter with tip projecting over the brachiocephalic vein, a right internal jugular central venous catheter with tip projecting over the superior vena cava (SVC), a Swan-Ganz (pulmonary artery) catheter, and residual pacing wires (with no pacemaker box!), and a well circumscribed ovoid opacity overlying the aortic knuckle.

Q2. Is the position of the pulmonary artery catheter correct?


The tip should be curved without loops/ kinks into a main pulmonary artery but not more peripheral than the junction between the medial and middle third of the ipsilateral lung.

Q3. What is the significance of the pacing wires?

Pre-operatively, the patient had a single lead left sided pacemaker (see CXR below). Occasionally pacing leads break on removing the pacemaker, resulting in retained leads in the chest. Most patients with retained leads have an uneventful course, so further attempts at removal are often not warranted. However, retained pacing wires have implications if the patient should subsequently need an MRI, as pacemaker leads can concentrate the radiofrequency energy resulting in local tissue heating. Retained venous pacing wires can lead to other complications such as thrombosis, infection, erosion or migration (e.g. embolisation).

Jao CXR 2b

Q4. What is the differential diagnosis of a superior mediastinal mass?

The causes of an anterosuperior mediastinal mass can be remembered by using the mnemonic 5 T’s: thymus, thyroid, thoracic aorta, terrible lymphoma, teratoma and germ cell tumours.

The ovoid opacity on CXR for this patient is not the aorta as you can see the aortic knuckle and descending aorta separate from this opacity (i.e. the ‘silhouette sign‘ is absent, as the outline of the aorta is still visible). Furthermore, the aorta is situated posteriorly so the mass must be more anterior.

In fact, this opacity was consistent with an anterior superior mediastinal mass demonstrated on a previous CT (see below). The CT demonstrates a well circumscribed homogenous collection measuring 6x5x6.3cm with Hounsfield value of 7HU which suggests a benign fluid collection. This was a long-standing cyst in the mediastinum that existed pre-operatively.

Jao CT 1b

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