phuluong2k
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60 y/o male with muscle weakness in his extremities, progressively difficulty in performing weight carrying task, 7 kg weight loss during the last 3 months, he smokes 2 packs/day. PE: muscle strength 3/5 in the proximal muscle groups symetrically, normal reflexes, normal sensory, Xray has a right lower lobe ill defined mass. What is the localization of the pathologic process in this patient ?
A. Peripheral nerve
B. Presynaptic membrane
C. Post synaptic membrane
D. Muscle membrane
E. Spinal cord
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| ARJ
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Muscle membrane
From UW
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| drvic
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this is Lambert Eaton Myasthenic Syndrome - a paraneoplastic syndrome seen with lung cancer (suggested by the smoking history and the Lower lobe lung mass and also the weight loss!) of the small cell variety. so obviously the pathology is the pre-synaptic membrane - because there is defective release of Ach in response to nerve stimulus...so that's why the muscle weakness....
one interesting thing about this syndrome....if you give repeated electrical stimuli to the motor nerves in such a patient, there is actually an INCREMENTAL response in contraction, in contrast to the usual decrease in response seen with Myasthenia Gravis....
treatment - plasmapheresis and immunosuppresive therapy (steroids and azathioprine)
hope this helps....
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| chemamr
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B
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| ARJ
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I got it wrong in UW by marking answer B few days back....
Lambert Eaton syndrome have absent or diminised reflexes at rest.
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| chemamr
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which is the answer phuluong???
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| drkpp
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it has to be eiher post synaptic mem. or the muscle membrane cause i am not sure of the difference between them.
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| frontal
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Wow, it's a good one. I'd say D (muscle membrane), because the features point toward a muscular dystrophy. (most show a proximal and symmetric muscle weakness. reflexes are normal unless the muscle mass is substantially reduced. sensory loss isn't found). As for the type, I'll need to check out dem books (shucks, I wish I knew more). I'm curious to know how the lung mass is related. On second thoughts, the answer may well not be D.
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| phuluong2k
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The given answer is muscle membrane, the explanation from UW is very unclear, any one can give more idea about this ?
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| frontal
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LEMS is not a possibility since, as AJR pointed out, the reflexes are diminished or absent in LEMS. Other features resemble those of m.gravis, so you expect ptosis and diplopia. Autonomic dysfunction and a dry mouth are also common.
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| chemamr
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 Good question.
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| frontal
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The diagnosis could be polymyositis and this would explain why the answer is D. There is a moderate increase in risk of malignancy including lung cancer, with polymyositis. The risk is highest at the time of diagnosis. In the chapter dealing with lung malignancies I read that polymyositis could be associated with them. Diagnosing in this case is rather tough and I was ready to believe that the lung mass thing was written to confuse us and was incidental in our case, when I read about this association. Anyway, they do not expect us to diagnose. It is obvious why peripheral neuropathy (you expect sensory loss and asymmetric signs), presynaptic membrane (features of m.gravis or LEMS are lacking) or spinal cord ( reflexes are unlikely to be normal), are not the answers. From the features, it appears primarily a muscular disease, so I'd go for D, even though I'm not sure what diseases and features to expect in the case of C.
Helps?
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| kal_9980
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keep it up frontal,with ur analysis of reasoning
really encouraging me learn more abt medicine,besides my tenshion for exams
thanks for all members of step-2ck esp forums r too good here
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kal
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| phuluong2k
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Frontal, your explanation is very good, thanks
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