A 66-year-old man presented with gradual decrease in food intake over a six-month period. Arm and leg movements gradually deteriorated, and he was placed on intravenous hyperalimentation at a previous clinic due to difficulties with oral intake. The patient was referred and admitted to our hospital for comprehensive examinations of decreased appetite and contractures of his arm and leg joints. On arrival, the patient presented with disorientation, muscle weakness of the extremities, limited extension of both shoulders and elbow joints, flexion contractures of both knee joints, orthostatic hypotension, and difficulty rolling over. Rehabilitation was started after admission to prevent progression of the joint contractures and disuse. Two months after admission, the patient went into shock with a high inflammatory response, hyponatremia, and hypoglycemia shown on blood tests. Acute adrenal insufficiency caused by severe infection was considered, and on the basis of endocrine tests, he was diagnosed as having isolated adrenocorticotropic hormone deficiency. Steroid replacement therapy was started, and his general condition and joint contractures of the elbow and knee joints improved. The patient then continued rehabilitation and was discharged home walking with cane assistance. In this condition, steroid treatment can improve the reversibility of joint contractures. Therefore, proactive rehabilitation should be considered along with steroid replacement therapy even if initiated a long time after onset.