The value of ultrasound in the diagnosis of limited scleroderma - a case report.

Systemic sclerosis, popularly referred to as scleroderma, is a chronic connective tissue disease with present autoantibodies against platelet-derived growth factor receptor. These antibodies activate directly fibroblasts causing the dermis and internal organs' fibrosis and vascular damage. Additionally, calcific collections, including hydroxyapatite crystals, may develop in subcutaneous tissue and juxta-articular soft tissue. Herein, we report a case of a 72-year-old woman, referred by a rheumatologist for plain radiography and ultrasound examination of hands due to pain and swelling of the fourth finger of the left hand. Dermal induration affecting hands, especially fourth finger on the left side and the Raynaud phenomenon were observed on physical examination. Furthermore, the patient had noticed periodic discharge with a toothpaste consistency from a tiny fistula localised in the vicinity of the fourth finger alterations. The paper emphasises a possible application of the twinkling artefact and MicroPure option on ultrasound examination in differential diagnosis of soft tissue calcifications. Making the correct diagnosis can attribute to precise planning of surgical treatment.

Introduction

Systemic sclerosis (SSc), popularly referred to as scleroderma, is a chronic connective tissue disease with present autoantibodies against platelet-derived growth factor receptor. These antibodies activate directly fibroblasts causing the dermis and internal organs’ fibrosis and vascular damage(.

Variants of scleroderma are the following:

limited cutaneous SSc (formely CREST syndrome);

diffuse cutaneous SSc;

SSc without skin involvement(.

The disease can manifest itself as skin changes only or may lead to multiple organ failure, i.e. pulmonary arterial hypertention, interstitial lung disease, renal failure, gastrointestinal disease, which depends on the clinical variant.

Clinical features of the former – limited systemic sclerosis (formely CREST syndrome), according to the acronym ‘CREST’, are: calcinosis, Raynaud phenomenon, esophageal dysmotility, sclerodactyly (thickening involving the skin of the fingers) and teleangiectasias (dilated capillaries).

According to the diversity of clinical manifestations and no radical treatment available for scleroderma, of the highest importance is early detection of internal organ involvement and adequate staging. Local surgical treatment for limited cutaneous SSc is based on the relation between calcifications and digits’ soft tissue, especially tendons and nerves.

Case report

A 72-year-old female patient with a clinical diagnosis of systemic sclerosis and Sjögren syndrome was referred by a rheumatologist for plain radiography and ultrasound examination of hands due to painful thickening and redness of the skin over the distal interphalangeal joint of the fourth finger of the left hand. The patient observed periodic discharge with a toothpaste consistency from a tiny fistula localised in the vicinity of the fourth finger alterations. Morover, dermal induration of the hands and the Raynaud phenomenon were discovered on physical examination.

Plain film radiography (PA projection) of the hands revealed a collection of coarse-grained calcifications in the soft tissue of the fourth finger of the left hand: over the distal phalanx, on the ulnar side of the distal interphalangeal (DIP) joint and over the distal part of the middle phalanx (Fig. 1, Fig. 2 A). Minor calcifications were visible on the ulnar side of the middle phalanx distal part in the corresponding finger of the right hand. Otherwise the image did not demonstrate any pathology.

Fig. 1

Plain film radiography (AP projection) of the hands reveals a collection of coarse-grained calcifications in the soft tissue of the left hand fourth digit and minor calcifications in the corresponding digit of the right hand (arrows)

Fig. 2

Comparison of the left hand fourth digit lesions: A. plain film radiography (AP projection) reveals a collection of coarse-grained calcifications in the soft tissue: at the distal phalanx, on the ulnar side of the DIP joint and the distal part of the middle phalanx; B. standard B-mode ultrasonography reveals a collection of minute hyperechogenic calcifications in soft the tissue on the palmar side of the fourth digit; C. positive power Doppler in the area of calcifications – the twinkling artifact

Afterwards, ultrasound examination of the hand was performed with Toshiba Aplio 500 using a linear PLT probe with a frequency of 18 MHz.

Standard B-mode ultrasonography revealed a 23 mm in lenght collection of hyperechogenic calcifications in the soft tissue on the palmar side of the fourth finger on the left side (Fig. 2 B). Fibers of flexor tendons of the fourth finger, flexor tendons sheath, retinacula, volar plates, proximal interphalangeal joint, distal interphalangeal joint and metacarpophalangeal joint were unremarkable.

In addition to standard B-mode imaging, colour and power Doppler were applied, which as a result of the twinkling artefact demonstrated colour pixels in the area of calcifications (Fig. 2 C).

Furthermore, modern MicroPure option available on Toshiba ultrasound scanners, which can be useful in detecting clustered microcalcifications not seen in B-mode imaging(, was adapted (Fig. 3). This option also allows differential diagnosis of microcalcifications in soft tissue. In our case, as the lesion was seen as slightly hyperechoic structures, it was not composed of microcalcifications (on the contrary to hyperechoic microcalcifications on MicroPure option imaging). Considering medical history, i.e. periodic discharge with a toothpaste consistency from a tiny fistula, hydroxyapatite (HA) deposits were suspected.

Fig. 3

MicroPure option, ultrasound examination of the left hand fourth digit: soft tissue deposits (on the left) seen as slightly hyperechoic structures on MicroPure option imaging (on the right, in blue)

No other pathologies of the hand were found.

Consulting orthopedist qualified the patient for surgical removal of lesions.

Discussion

Systemic sclerosis is a chronic connective tissue disease affecting the skin or internal organs. A clinical variant with a benign course is called limited systemic sclerosis (formely CREST syndrome). In our case, 3 out of 5 aforementioned features of a “CREST” syndrome were present (except E and T).

Plain radiography, as far as systemic sclerosis is concerned, plays a crucial role in the diagnosis of soft tissue calcifications and acroosteolysis. Radiographs of our patient's hands revealed a collection of coarse-grained calcifications in the soft tissue of the fourth finger of the left hand and less pronounced lesions in the corresponding finger of the right hand.

As far as limited cutaneous SSc is concerned, soft tissue calcific collections are typically para-articular, i.e. they do not communicate with the joint. According to the literature they have amorphous appearance(, yet in our own practice we have usually observed coarse-grained lesions (unlike linear deposits along muscles and fasciae observed in dermatomyositis). In about 25% of patients with scleroderma they are composed of hydroxyapatites that can be released from calcific collections(. Most commonly they deposit in the areas of repeated microtrauma (compression), i.e. digital pulp, buttocks, the elbow region, posterior part of the forearm or in the prepatellar area.

The presence of calcifications, seen on X-ray as hyperechogenic lesions, can be confirmed with the use of MicroPure option, which has already been used in detecting microcalcifications in breast tissue and monosodium urate crystals in gouty arthritis(. In our case, application of MicroPure option on ultrasound examination allowed detection of ‘soft’ calcifications, which was indicative of HA rather than calcific deposits. Thus, MicroPure option can be adapted to differentiate HA crystals from other calcifications, yet the final diagnosis would only be available when comparing the ultrasonographic image with the chemical composition analysis of the lesion.

Furthermore, colour and power Doppler examination detected colour pixels, which was an effect of the twinkling artefact rather than soft tissue inflammation caused by crystal deposits. The twinkling artifact is the phenomenon observed on colour and power Doppler examination immediately behind a stationary echogenic surfaces, such as urinary tract stones, soft tissue calcific deposits or bones, acquiring a false appearance of blood flow. However, inability to detect a flow on spectral Doppler indicates its artifactual nature. This phenomenon, considering uneven and rough surface, usually occurs when Doppler scale settings are high and ultrasound beams of low-frequency are being transmitted(. According to Wei Lu et al., this effect is caused by small air bubbles entrapped in cracks and crevices of rugged surfaces(.

Application of the twinkling artifact (‘colour comet-tail artifact’) in clinical practice allows urinary tract deposits detection or, less frequently, cholelithiasis and biliary lithiasis(. It also provides detection of minute calcific deposits before their size is capable of eliciting an acoustic shadow. As it can mimic blood flow on ultrasound examination, the twinkling artifact effect is worth remembering(.

Subcutaneous HA deposits can lead to local inflammation, if severe to ulceration or as we present in our case to dermal fistula. However, other features of limited scleroderma, such as acroosteolysis (resorption of distal bony phalangeal tuft) associated with calcinosis or soft tissue atrophy most frequently observed with the Raynaud phenomenon, were not reported.

Conclusion

The course of the disease is rather benign and depends on organ involvement. Subcutaneous tissue deposits occur as calcifications and hydroxyapatites crystals. Imaging modality of choice is plain radiography. Clinically indicated, ultrasound examination reveales the relation between calcifications and soft tissue of the hands, especially tendons, retinacula and neurovascular bundles.