A 24-year-old man was referred to our clinic in August 2003 with complaints of weakness, dizziness, and bilateral knee pain of 3 years' duration. Bilateral digital clubbing had been found on routine physical examination during his military service 4 years earlier. There were no cardiorespiratory or abdominal symptoms. There was no compromise in the activities of everyday life. The patient was not a chronic smoker. In the family history of the patient, his brother had been diagnosed with pachydermoperiostosis in another center 2 years earlier, but did not return to the hospital for a follow-up investigation of myelofibrosis. On physical examination, the patient showed marked drumstick clubbing of the hands (Fig. 1), and a pale general appearance. The causes of digital clubbing are shown in Table 1 (Fawcett RS, Linford S, Stulberg DL. Nail abnormalities: clues to systemic disease. Am Fam Physician 2004; 69: 1417-1424). Deep nasolabial folds were seen on the face. Skin hypertrophy, cutis verticis gyrata, and seborrhea on the face were also observed. The patient also complained of hyperhidrosis. Examination of the cardiovascular system was normal. There was bilateral swelling of the ankle and knee (Fig. 2). Hepatosplenomegaly was found on abdominal examination. Investigations showed hypochromic microcytic anemia [hemoglobin, 8.58 g/dL (normal, 12.2-18.1 g/dL); hematocrit, 28.1% (normal, 37.7-53.7%); white blood cell count, 3430/mm(3) (normal, 4600-10,200/mm(3)); neutrophils, 2470/mm(3) (normal, 2000-6900/mm(3)); lymphocytes, 820/mm(3) (normal, 600-3400/mm(3)); platelets, 162,000/mm(3) (normal, 142,000-424,000 mm(3)); mean corpuscular volume, 73.7 fL (normal, 80-97 fL)]. Anisocytosis, poikilocytosis, microcytosis, and hypochromia were observed on peripheral blood examination, and the erythrocyte sedimentation rate was 37 mm/h. The serum C-reactive protein level was 50.1 mg/L (normal, 0-5 mg/L). Biochemical parameters, including serum calcium, phosphate, alkaline phosphates and liver function tests, were found to be within the normal range. The causes of secondary hypertrophic osteoarthropathy associated with pulmonary, rheumatologic, endocrine, cardiac, and gastroenterologic disorders were excluded. Growth hormone level and thyroid function tests were normal. Antinuclear antibody, TORCH [Toxoplasma immunoglobulin M (IgM), rubella IgM, cytomegalovirus IgM, herpes simplex IgM] panel, and markers of hepatitis were negative. Serum Igs and rheumatoid factor were found to be within the normal range. There was subperiosteal new bone formation on bilateral knee X-ray (Fig. 3). Radiography of the chest, pulmonary function tests, arterial blood gas, and echocardiography were normal. Abdominal ultrasonography revealed hepatosplenomegaly. Amyloid deposition was not determined in rectal biopsy. Reticulin-type myelofibrosis was found on bone marrow biopsy (Figs 4 and 5). In the cytogenetic study, monosomy 22 was detected in four of 20 metaphase plates.