A 60-year-old man comes to the office due to fatigue and muscle weakness in his extremities. The weakness has gotten progressively worse over the past few months. He has also lost 7 kg (15.4 lb) during the last 3 months. He has no other medical conditions. The patient smokes 2 packs of cigarettes daily and consumes alcohol occasionally. On examination, he has difficulty getting out of the chair to sit on the examining table. Muscle strength is 3/5 in the proximal muscle groups symmetrically and is not improved by repeated muscle contractions. Reflexes are 2+ bilaterally. No sensory abnormality is present. There are erythematous patches and violaceous papules involving the dorsum of his fingers. Chest x-ray reveals an ill-defined mass in the right lower lobe. The patient's muscle weakness is most likely due to a pathologic process at which of the following?

Question

A 60-year-old man comes to the office due to fatigue and muscle weakness in his extremities.  The weakness has gotten progressively worse over the past few months.  He has also lost 7 kg (15.4 lb) during the last 3 months.  He has no other medical conditions.  The patient smokes 2 packs of cigarettes daily and consumes alcohol occasionally.  On examination, he has difficulty getting out of the chair to sit on the examining table.  Muscle strength is 3/5 in the proximal muscle groups symmetrically and is not improved by repeated muscle contractions.  Reflexes are 2+ bilaterally.  No sensory abnormality is present.  There are erythematous patches and violaceous papules involving the dorsum of his fingers.  Chest x-ray reveals an ill-defined mass in the right lower lobe.  The patient's muscle weakness is most likely due to a pathologic process at which of the following?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d123_e44c_bc81_67589f4e4c70_MD0003_00 This patient's smoking history, weight loss, and right lower lobe mass are concerning for lung cancer. Patients with malignancy can develop a paraneoplastic syndrome due to the tumor producing hormones, cytokines, or cross-reactive antibodies (eg, shared antigens between proteins expressed on tumor cells and human cells). Therefore, paraneoplastic syndromes are not directly related to the cancer's invasion. They are most commonly seen in cancers of the lung, breast, and ovaries and in lymphomas. Manifestations typically resemble those of primary endocrine, metabolic, hematologic, or neuromuscular disorders. Paraneoplastic syndromes affecting the peripheral nerve and/or muscle (eg, myasthenia gravis, Lambert-Eaton syndrome, dermatomyositis) most commonly present with muscle weakness, as seen in this patient. This patient likely has dermatomyositis, an idiopathic inflammatory myopathy with immune-mediated muscle fiber injury. It typically presents with symmetrical, proximal muscle weakness and an erythematous rash on the dorsum of the fingers (Gottron sign) and/or upper eyelids (heliotrope eruption). Diagnosis is usually confirmed by muscle biopsy. (Gottron sign) upper eyelids (heliotrope eruption) Other paraneoplastic syndromes include the following: Myasthenia gravis, which is due to autoantibodies against acetylcholine receptors in the postsynaptic membrane. It is characterized by fluctuating ocular (ptosis, diplopia), facial, and/or bulbar muscle weakness that becomes worse with repetitive tasks. This patient's skin findings and absence of eye findings make myasthenia gravis less likely (Choice C). Lambert-Eaton myasthenic syndrome, which involves antibodies targeted against the presynaptic membrane. Although patients can also exhibit proximal limb muscle weakness, they usually have other autonomic dysfunction (eg, dry mouth, erectile dysfunction) and absent or diminished deep-tendon reflexes. Repeat isometric contraction can lead to temporary improvement of muscle weakness and reappearance of absent deep-tendon reflexes. This patient's preserved reflexes, skin findings, and lack of improvement with repeat muscle contractions are more consistent with dermatomyositis (Choice D). Paraneoplastic myelopathy of the spinal cord, which typically presents with flaccid or spastic paraplegia or quadriplegia, sensory deficits, and/or urinary or fecal retention/incontinence (Choice E). (Choice B) Peripheral nerve involvement usually causes neuropathies presenting with sensory and/or motor abnormalities and abnormal reflexes on physical examination. This patient's normal reflexes and sensory examination make this unlikely. Educational objective: Dermatomyositis is an idiopathic inflammatory myopathy with immune-mediated muscle injury that can be due to a paraneoplastic syndrome in malignancy. Patients typically have symmetrical, proximal muscle weakness and an erythematous rash over the dorsum of the fingers (Gottron sign) and/or upper eyelids (heliotrope rash). References: Paraneoplastic muscle disease. (http://www.ncbi.nlm.nih.gov/pubmed/21444019)

A 60-Year-Old Man Comes to the Office Due to Fatigue