Forearm lump and osteoporosis

We introduce a case of a menopausal woman newly diagnosed with primary osteoporosis who has been detected with a forearm lump. A 57-year old female is confirmed with osteoporosis at DXA. The patient developed within 10 days a painful lump with local redness at dorso-medial part of left forearm. Apparently no local trauma was identified. Neither had she a general infection or any other condition in the mean time. The ultrasound identified a hypoechoic area of 4 by 1.3 by 4 cm, with positive Doppler signal. A local infection was considered and she was offered antibiotics for 10 days. However, since the patient also accused bone pain, she was re-referred for an endocrine assessment. The hormonal panel was consistent with the first assays. Also a mild inflammatory syndrome was detected based on erythrocytes sedimentation rate of 31 mm/1-hour (normal: < 25 mm/1-h) and C reactive protein of 1.4 mg/dl (normal: < 1 ng/ml). An X Ray of the region was done and showed no anomaly. The bone whole body scintigram was negative at forearm but a fracture rib at the level of 9th left rib was identified and considered osteoporotic. A computed tomography showed the subcutaneous localisation of the lump with small calcifications and no bone involvement. Paget’s disease of the bone was excluded based on normal bone turnover markers and negative bone scintigram. The proximity with a bone disease diagnosis needs to differentiate a subcutaneous lesion from a potential bone deformity caused by a metabolic bone condition.


IntroductIon
Osteoporosis is a complex dual disease of the bone (1,2). Except for kyphosis and the fragility fractures themselves there is not a specific skin sign associated with this condition, neither a bone deformity except for potential spine anomalies due to vertebral fractures (3,4). However, bone metabolic conditions like Paget's disease need to be differentiated from osteoporosis and bone deformities might be found in this particular situation (5,6).

AIm
Our purpose is to introduce a case of a menopausal woman newly diagnosed with primary osteoporosis who has been detected with a forearm lump of apparently unknown origin.

mAterIAl And method
This is a case report. Clinical, endocrine and imaging data are introduced.

cAse report
This is a 57 year old female referred after general practitioner and gynaecological exam suspected osteoporosis. One year ago she suffered a unilateral low-trauma should fracture. She had spontaneous menopause at age of 50 years with no hormonal replacement therapy. The clinical exam was within normal limits for age at first evaluation. Blood tests revealed normal biochemistry parameters like ionic calcium of 4 mg/dl (normal: 3.9-4.9 mg/dl), and bone turnover markers of formation as osteocalcin of 19 ng/ml (normal: 15-46 ng/ml), and alkaline phosphatase of 80 U/l (normal: 38-105 U/l), but also a mild suppression of blood bone resorption maker CrossLaps of 0.146 ng/ml (normal: 0.33-0.782 ng/ml). She had normal thyroid and adrenal function. No vitamin D deficiency was identified (she had a 25-hydroxyvitamin D of 30 ng/ml and parathormone of 32 pg/ ml, normal levels between 15 and 65 pg/ml).
Central DXA (Dual-Energy X-Ray Absorptiometry) showed a bone mineral density (BMD) at the lumbar spine of 0.743 g/sqcm, T-score of -3.6 SD (standard deviation), a Z-score of -2.5 SD, femoral neck BMD of 0.677 g/sqcm, T-score of -2.6 SD, Z-score of -1.4 SD, total hip BMD of 0.67 g/sqcm, T-score of -2.7 SD, Z-score of -1.8 SD, left (non-dominant arm) third distal radius BMD of 0.592 g/sqcm, T-score of -1.7 SD, Z-score of -1.2 SD. These data are consistent with the diagnosis of osteoporosis which was already clinically suspected based on previous fragility fracture. The screening profile X-Ray of the spine was negative for others fractures.
After the diagnosis of primary complicated osteoporosis was established specific medication was recommended with oral bisphosphonates (weekly alendronate) and supplements with vitamin D and calcium. Soon the patient developed (within 10 days) at the level of left forearm a painful lump with local redness. Apparently no local trauma was identified by the patient before or during the lump growth. Neither had she had a general infection or any other condition in the mean time. The lesion had 3 cm (centimetre) diameter and it was located at the level of third dorso-medial part of the forearm. The local ultrasound identified a hypoechoic area of 4 by 1.3 by 4 cm, with positive Doppler signal (Figure 1). A local infection was considered and she was offered antibiotics for 10 days. However, since the patient also accused bone pain, she was re-referred for an endocrine assessment. The hormonal panel was consistent with the first assays. Also a mild inflammatory syndrome was detected based on erythrocytes sedimentation rate of 31 mm/1-hour (normal less than 25 mm/1-h) and C reactive protein of 1.4 mg/ dL (normal: 0-1 ng/ml). An X-Ray of the region was done and showed no anomaly. The bone whole body scintigram was negative at the level of the lump region except for a newly diagnosed fracture rib at the level of 9 th left rib which was considered also osteoporotic. A computed tomography showed the subcutaneous localisation of the lump with small calcifications and no bone involvement (Figure 2). Paget's disease of the bone was excluded and the diagnosis of menopausal osteoporosis was considered accidental. No change of prior recommendations regarding osteoporosis was done. Further periodic assessment is necessary.

dIscussIon
Paget's disease of the bone has focal, single or multiple lesions with a relative slow progression affecting bone, joints and vascular areas (7). It has a relative high frequency in some populations but less than primary osteoporosis (7). Bone deformities as it might have been in this case are identified especially in pressure areas (8,9,10). Serum total alkaline phosphatase remains the first line of assays even less than on fifths of cases had normal values (5,10,11). In this case the bone turnover were within normal limits except for a small decrease of CrossLaps. Generally the bone turnover markers are considered with a high inter-and intra-individual variability (12,13). The derivates from collagen are most useful in daily practice (12,13,14). A recent fracture increases the bone markers for a while and they are not useful for establishing the diagnosis of osteoporosis (12). In Paget's disease or multiple myeloma the markers may reach to extremely high values (10,12). Under biphosphonates the markers get low opposite to teriparatide therapy as an osteoanabolic option (13,14,15). In this case we do not currently consider clinically relevant the value of CrossLaps.
Radionuclide bone scans are useful for positive diagnosis and for differential diagnosis as seen here regarding bone metabolic conditions (5,10). Even a prior undetected fracture was identified at the rib the region with deformation was not active. Yet, there are authors who do not consider that the use of bone scintigraphy is as relevant in order to change the evaluation on patients with limb pain which is suspected to be connected with a musculoskeletal condition (18).
Local pain may be the first sign that allows the condition's detection based on clinical approach (5,10). Another interesting differential diagnosis of the forearm lump might be a muscle metastasis (19,20). There are only a few reports in the literature (19,20). Direct muscle invasion from a cancer is atypical (19,20). A case of a women with previous breast cancer identified a biceps metastasis which was treated with local radiotherapy (19). Another series of 205 patients with oesophageal cancer revealed 4 subjects with skeletal muscle metastasis based on PET/CT (positron emission tomography/computed tomography) scan (20). Fortunately this was not the case here even it was taken into consideration at the begging of re-assessment as a differential diagnosis.

conclusIon
The proximity with a bone disease diagnosis needs to differentiate a subcutaneous lesion from a potential bone deformity caused by a metabolic bone condition.