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Patient Case: Mixed Connective Tissue Disease

Patient Case: Mixed Connective Tissue Disease

Discussion

A 50-year-old woman presents to a rheumatology clinic with a six-month history of progressive skin thickening on her hands and forearms, along with Raynaud’s phenomenon. She also reports difficulty swallowing solid foods and occasional shortness of breath. On examination, she has sclerodactyly and mild digital pitting scars, but no significant facial skin tightening.

Serologic testing reveals a negative anti-centromere and anti-Scl-70 antibody profile. However, her inflammatory markers are mildly elevated, and her creatine kinase (CK) levels are significantly increased. Nailfold capillaroscopy does not show the typical findings of systemic sclerosis. A high-resolution CT scan of the chest shows mild interstitial lung disease, and an esophageal manometry test confirms hypomotility.

Given her presentation, an alternative diagnosis such as mixed connective tissue disease (MCTD) or dermatomyositis with systemic sclerosis-like features is considered. Further testing reveals positive anti-U1 RNP antibodies, supporting a diagnosis of MCTD. She is started on immunosuppressive therapy, including low-dose corticosteroids and methotrexate, with close monitoring of her lung function.

Questions
1. Which feature in this patient raises suspicion for a systemic sclerosis mimic rather than true systemic sclerosis?

A) Raynaud’s phenomenon

B) Negative anti-centromere and anti-Scl-70 antibodies

C) Esophageal hypomotility

D) Sclerodactyly

2. Which additional test result helped confirm the diagnosis of mixed connective tissue disease (MCTD) in this patient?

A) Positive anti-U1 RNP antibodies

B) Positive anti-Scl-70 antibodies

C) Presence of nailfold capillary abnormalities

D) Low complement levels

3. What is the most likely cause of the patient’s muscle weakness and elevated creatine kinase (CK) levels?

A) Interstitial lung disease

B) Dermatomyositis overlap

C) Scleroderma renal crisis

D) Drug-induced myositis

4. What is the most appropriate treatment approach for this patient?

A) Calcium channel blockers alone

B) High-dose corticosteroids only

C) Low-dose corticosteroids and methotrexate

D) Antibiotics and proton pump inhibitors

Reveal answers

Answers

1 - B) Negative anti-centromere and anti-Scl-70 antibodies

Systemic sclerosis is often associated with either anti-centromere (limited form) or anti-Scl-70 (diffuse form) antibodies. Their absence, along with overlapping symptoms, suggests a systemic sclerosis mimic such as MCTD or dermatomyositis.

2 - A) Positive anti-U1 RNP antibodies

Anti-U1 RNP antibodies are the hallmark of MCTD, which can present with features of systemic sclerosis, lupus, and polymyositis. Their presence helps distinguish MCTD from other connective tissue diseases.

3 - B) Dermatomyositis overlap

Elevated CK levels suggest muscle involvement, which is uncommon in systemic sclerosis but seen in overlap syndromes like MCTD or dermatomyositis. The presence of interstitial lung disease further supports myositis-related connective tissue disease.

4 - C) Low-dose corticosteroids and methotrexate

Treatment in overlap syndromes involves managing systemic inflammation and autoimmune features. Low-dose corticosteroids and methotrexate help control muscle and joint involvement while minimizing the risk of complications like scleroderma renal crisis.

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