Diagnosis
CIP and CIM are a major cause of ICU-acquired weakness (ICUAW). Current guidelines recommend a clinical diagnosis of ICUAW, made by manually testing the muscle strength with the use of the Medical Research Council (MRC) sum score or handgrip dynamometry.CIP/CIM is often not identified until a patient is unable to be successfully weaned from a mechanical ventilator. Early detection of the condition is difficult, because these patients are often sedated and intubated, and thus unable to cooperate with a thorough neuromuscular physical examination. The use of conventional nerve conduction studies is time-consuming and requires specialized personnel; however, simplified electrophysiologic tests can be used as screening tools in the critically ill to confirm or exclude CIP/CIM. The peroneal nerve test is a validated, high-sensitivity, minimally invasive, non-volitional and quick diagnostic test which can accurately exclude CIP/CIM if the result is normal. Moreover, patients with disuse atrophy and muscle deconditioning have normal electrophysiological tests even if muscle strength is severely reduced Hence, these tests are important to define the cause of muscle weakness and can be helpful to refine the prognosis. Laboratory values
The serum creatine phosphokinase (CPK) can be mildly elevated. While the CPK is often a good marker for damage to muscle tissue, it is not a helpful marker in CIP/CIM, because CIP/CIM is a gradual process and does not usually involve significant muscle cell death (necrosis). Also, even if necrosis is present, it may be brief and is therefore easily missed.
Finally an intramolecular attack from the hydroxyl group of C2 to the carboxylic acid group closes the ring and forms the lactone umbelliferone. Synthesis of methoxsalen
The biosynthetic route then continues with the activation of dimethylallyl pyrophosphate (DMAPP), produced via the mevalonate pathway, to form a carbo-cation via the cleavage of the diphosphates. Once activated, the enzyme umbelliferone 6-prenyltransferase catalyzes a C-alkylation between DMAPP and umbelliferone at the activated position ortho to the phenol, yielding demethylsuberosin. This is then followed by a hydroxylation catalyzed by the enzyme marmesin synthase to yield marmesin. Another hydroxylation is catalyzed by psoralen synthase to yield psoralen. A third hydroxylation by the enzyme psoralen 8-monooxygenase yields xanthotoxol which is followed by a methylation via the enzyme xanthotoxol O-methyltransferase and S-adenosyl methionine to yield methoxsalen. Risks and side effects
Patients with high blood pressure or a history of liver problems are at risk for inflammation and irreparable damage to both liver and skin. The eyes must be protected from UVA radiation. Side effects include nausea, headaches, dizziness, and in rare cases insomnia. Methoxsalen has also been classified as an IARC Group 1 carcinogen (known to cause cancer) but is only cancerous when combined with light - UVA radiation. Society and culture
Author John Howard Griffin (1920–1980) used the chemical to darken his skin in order to investigate racial segregation in the American South. He wrote the book Black Like Me (1961) about his experiences. References
External links
"Methoxsalen". Drug Information Portal. U.S. National Library of Medicine.